#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int N = 100010;
int n, m, k;
struct Edge{
    int a,b,w;
}edges[N];
int dist[N], backup[N];
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; // n个点,最多经过k条边
    for(int i = 0;i < m;i++)
    {
        int a,b,w;
        cin >> a >> b >> w;
        edges[i] = {a,b,w};
    }
    int s = bellman_ford();
    if(s == -1) puts("impossible");
    else cout << dist[n]<<endl;
    return 0;
}