#include<iostream>
#include<cstring>
using namespace std;

const int N = 510, M = 10010;

int n, m, k;
int dist[N], backup[N];

struct Edge
{
    int a, b, w;
} edges[M];

int bellman_ford()
{
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    for (int i = 0; i < k; i ++ )
    {
        memcpy(backup, dist, sizeof dist);
        for (int j = 0; j < m; j ++ )
        {
            int a = edges[j].a, b = edges[j].b, w = edges[j].w; 
            dist[b] = min(dist[b], backup[a] + w);            
        }
    }
    if (dist[n] > 0x3f3f3f3f / 2) return -1;
    return dist[n];
}

int main()
{
    cin >> n >> m >> k;

    for (int i = 0; i < m; i ++ )
    {
        cin >> edges[i].a >> edges[i].b >> edges[i].w;

    }

    int t = bellman_ford();
    if (t == -1) cout << "impossible" << endl;
    else cout << t;
    return 0;

}

#include <cstring>
#include <iostream>
#include <queue>
#include <algorithm>

using namespace std;

const int N = 160010;
typedef pair<int, int> PII;

int n, m;
int e[N], w[N], h[N], ne[N], idx;
int dist[N];
bool st[N];

void add (int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;
}

int dijkstra()
{
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> q;
    q.push({0, 1});

    while (q.size())
    {
        auto t = q.top();
        q.pop();
        int distance = t.first, ver = t.second;

        if (st[ver]) continue;
        st[ver] = true;

        for (int i = h[ver]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > distance + w[i]) 
            {
                dist[j] = distance + w[i];
                q.push({dist[j], j});
            }
            // 如果dist[j] <= distance + w[i]说明存在一个 dist[j] 比当前的，利用最优点更新dist[j]的结果还要小；
            // 因此该点j存在两个情况
            // 1、已经放入st中，那么q.push在不在if语句中结果都一样，会在下次选择到的时候continue掉，push在if语句中会少执行一次；
            // 2、还未放入st中，那么这个点之前被更新过一次，只要之前更新了就一定会放入q中，那么再讲j放入q中则多做了一次；
            // 简而言之，每次只找到最优的点并只push能够利用最优点进行更新的点即可，若不能更新则不用管；

        }
    }

    if (dist[n] == 0x3f3f3f3f) return -1;

    return dist[n];


}

int main()
{
    scanf("%d%d", &n, &m);

    memset(h, -1, sizeof h);

    while (m -- )
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c);
    }

    cout << dijkstra() << endl;

    return 0;
}

#include<iostream>
#include<queue>
#include<cstring>
#include<unordered_map>
using namespace std;
const int N = 100010;
int h[N], e[N], ne[N], idx = 0;
int n, m;
int d[N];
bool st[N];
void add (int a, int b)
{
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx ++ ;
}

int bfs()
{
    queue<int> q;
    q.push(1);
    memset(d, -1, sizeof d);
    d[1] = 0;
    while(q.size())
    {
        auto t = q.front();
        q.pop();
        for(int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];

            if(d[j] == -1)
            {
                d[j] = d[t] + 1;
                q.push(j);
            }
        }
    }

    return d[n];
}

int main(){
    cin >> n >> m;
    int a, b;
    memset(h, - 1, sizeof h);
    for(int i = 0; i < m; i ++ )
    {
        cin >> a >> b;

        add(a, b);
    }

    cout << bfs() ;
    return 0;
}

#include<iostream>
#include<queue>
#include<cstring>
#include<vector>
using namespace std;

const int N = 100010;

int h[N], e[N], ne[N], d[N], idx;
int n, m;
bool st[N];

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

int main()
{
    memset(h, -1, sizeof h);
    cin >> n >> m;
    int a, b;
    queue<int> q;
    for (int i = 0; i < m; i ++ )
    {
        cin >> a >> b;
        add(a, b);
        d[b] += 1;
    }
    vector<int> ans;
    int cnt = 0;

    for (int i = 1; i <= n; i ++ )
    {
        if (d[i] == 0) 
        {
            cnt ++ ;
            q.push(i);
            ans.push_back(i);
        }
    }

    // for (int i = 1; i <= n; i ++ ) cout << d[i] << ' ';
    // cout << endl;


    while (q.size())
    {
        auto t = q.front();
        q.pop();

        for (int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            d[j] -= 1;
            // if (t == 2) cout << j << d[j] << ' ' << endl;
            if (d[j] == 0)
            {
                // if (t == 2) cout << j;
                ans.push_back(j);
                q.push(j);
                cnt ++ ;

            }
        }
    }
    // cout << cnt;
    if (cnt == n)
    {
        for (int i = 0; i < n; i ++ ) cout << ans[i] << ' ' ;
        cout << endl;
    }
    else cout << -1 << endl;
    return 0;

}

#include<iostream>
#include<cstring>
using namespace std;

const int N = 100010, M = N * 2;

int h[N], e[M], ne[M], idx;
bool st[N];
int n, ans = N;

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

int dfs(int u)
{
    st[u] = true;
    int sum = 1, res = 0;
    for (int i = h[u]; i != -1; i = ne[i])
    {
        int j = e[i];
        if (!st[j])
        {
            int s = dfs(j);
            res = max(res, s);
            sum += s;
        }
    }
    res = max(res, n - sum);
    ans = min(ans, res);
    return sum;
}

int main()
{
    cin >> n;
    memset(h, -1, sizeof h);
    int a, b;
    for (int i = 0; i < n; i ++ )
    {
        cin >> a >> b;
        add(a, b);
        add(b, a);
    }
    dfs(1);
    cout << ans << endl;
    return 0;
}

#include <iostream>

using namespace std;

const int N = 100010, M = 1000010;

int n, m;
int ne[N];
char s[M], p[N];

int main()
{
    cin >> n >> p + 1 >> m >> s + 1;

    // for (int i = 2, j = 0; i <= n; i ++ )
    // {
    //     while (j && p[i] != p[j + 1]) j = ne[j];
    //     if (p[i] == p[j + 1]) j ++ ;
    //     ne[i] = j;
    // }

    // for (int i = 1, j = 0; i <= m; i ++ )
    // {
    //     while (j && s[i] != p[j + 1]) j = ne[j];
    //     if (s[i] == p[j + 1]) j ++ ;
    //     if (j == n)
    //     {
    //         printf("%d ", i - n);
    //         j = ne[j];
    //     }
    // }

    for (int i = 2, j = 0; i <= n; i ++ )
    {
        while (j && p[i] != p[j + 1]) j = ne[j];
        if (p[i] == p[j + 1]) j ++ ;
        ne[i] = j;
    }

    for (int i = 1, j = 0; i <= m; i ++ )
    {
        while (j && s[i] != p[j + 1]) j = ne[j];
        if (s[i] == p[j + 1]) j ++ ;
        if (j == n)
        {
            printf("%d ", i - n);
            j = ne[j];
        }
    }

    return 0;
}

#include <iostream>

using namespace std;

const int N = 100010;

int stk[N], tt;

int main()
{
    int n;
    cin >> n;
    while (n -- )
    {
        int x;
        scanf("%d", &x);
        while (tt && stk[tt] >= x) tt -- ;
        if (!tt) printf("-1 ");
        else printf("%d ", stk[tt]);
        stk[ ++ tt] = x;
    }

    return 0;
}

#include <iostream>

using namespace std;

const int N = 1000010;

int a[N], q[N];

int main()
{
    int n, k;
    scanf("%d%d", &n, &k);
    for (int i = 0; i < n; i ++ ) scanf("%d", &a[i]);

    int hh = 0, tt = -1;
    for (int i = 0; i < n; i ++ )
    {
        if (hh <= tt && i - k + 1 > q[hh]) hh ++ ;

        while (hh <= tt && a[q[tt]] >= a[i]) tt -- ;
        q[ ++ tt] = i;

        if (i >= k - 1) printf("%d ", a[q[hh]]);
    }

    puts("");

    hh = 0, tt = -1;
    for (int i = 0; i < n; i ++ )
    {
        if (hh <= tt && i - k + 1 > q[hh]) hh ++ ;

        while (hh <= tt && a[q[tt]] <= a[i]) tt -- ;
        q[ ++ tt] = i;

        if (i >= k - 1) printf("%d ", a[q[hh]]);
    }

    puts("");

    return 0;
}

#include<iostream>
#include<algorithm>

const int N = 50010;

using namespace std;

int n;

struct R
{
    int w, s;
    bool operator <(const R &W)const
    {
        return w + s > W.w + W.s;
    }
}r[N];

int main()
{
    cin >> n;
    for (int i = 0; i < n; i ++ ) cin >> r[i].w >> r[i].s;
    sort(r, r + n);
    int res = -2e9, sum = 0;
    for (int i = n - 1; i >= 0; i -- ) 
    {
        // cout << r[i].w << endl;
        res = max(res, sum - r[i].s);
        sum += r[i].w;
    }
    cout << res;
    return 0;

}

#include<iostream>
#include<algorithm>
using namespace std;
int p[100010];
int main()
{
    int n;
    cin >> n;
    for(int i = 0; i < n;  i ++ ) cin >> p[i];
    sort(p, p + n);
    int md = p[n/2];
    int res = 0 ;
    for(int i = 0; i < n; i ++ ) res += abs(p[i] - md);
    cout << res;
    return 0;
}