#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int N = 510, M = 10010;
int n, m, k;
int dis[N], last[N];

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

void bellman_ford() {
    memset(dis, 0x3f, sizeof(dis));
    dis[1] = 0;

    for (int i = 0; i < k; i++) {
        memcpy(last, dis, sizeof(dis));
        for (int j = 0; j < m; j++) {
            auto t = edges[j];
            dis[t.b] = min(dis[t.b], last[t.a] + t.c);
        }
    }
}

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

    for (int i = 0; i < m; i++) {
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);
        edges[i] = {a, b, c};
    }

    bellman_ford();

    if (dis[n] > 0x3f3f3f3f / 2) cout << "impossible" << endl;
    else cout << dis[n] << endl;

    return 0;
}