#include <bits/stdc++.h>

using namespace std;

const int N = 505, M = 10005;

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

struct Node{
    int a, b, w;
}edge[M];

int bellman_ford(){
    memset(dis, 0x3f, sizeof(dis));

    dis[1] = 0;

    for(int i = 0; i < k; i++){
        memcpy(backup, dis, sizeof(dis));

        for(int j = 0; j < m; j++){
            int a = edge[j].a, b = edge[j].b, w = edge[j].w;
            dis[b] = min(dis[b], backup[a] + w); //备份，防止原来的数据被覆盖
        }
    }
    if(dis[n] > 0x3f3f3f3f / 2) return -1;
    return dis[n];
}

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};
    }

    int t = bellman_ford();

    if(t == -1) puts("impossible");
    else printf("%d\n", t);
}