#include <iostream>
#include <cstring>
#include <algorithm>
const int N = 507,M = 1e4+7;
using namespace std;
int n, m, k, res;
struct Edge
{
int a, b, w;
} edge[M];
int dist[M],backup[M];
void ballman_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=edge[j].a,b=edge[j].b,w=edge[j].w;
dist[b]=min(dist[b],backup[a]+w);
}
}
if(dist[n] > 0x3f3f3f3f / 2) puts("impossible");
else cout << dist[n];
return ;
}
int main()
{
scanf("%d%d%d",&n,&m,&k);
for(int i=0;i<m;i++)
{
int a, b, w;
scanf("%d%d%d",&a,&b,&w);
edge[i]={a, b, w};
}
ballman_ford();
return 0;
}