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

using namespace std;

const int N = 510, M = 10010;
int n, m, k;
int dist[N];        //每个点到起点的距离数组
int backup[N];      //记录上一次结果的数组
struct Edge         //定义结构体来存储
{
    int a, b, w;
}edges[M];

int bellman_ford()
{
    memset(dist, 0x3f, sizeof dist);        //初始化距离
    dist[1] = 0;
    for ( int i = 0; i < k; i ++ )          //进行k次迭代
    {
        memcpy(backup, dist, sizeof dist);  //备份距离数组，用上一次的距离更新新的距离
        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 ++ )
    {
        int a, b, w;
        cin >> a >> b >> w;
        edges[i] = {a, b, w};
    }

    int t = bellman_ford();

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