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

using namespace std;

const int N = 510, M = 10010;

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

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

int bellman_ford()
{
    memset(dist, 0x3f, sizeof dist);       // 
    dist[1] = 0;                           // 初始这两行基本不变 

    for (int i = 0; i < k; i ++)    // k 次 循环保证路径上的边数少于n行
    {
        memcpy(backup, dist, sizeof dist);   //每次先备份
        for (int j = 0; j < m; j ++)
        {
            int a = edges[j].a,b = edges[j].b, w= edges[j].w;   // 获取每一条边的信息
            dist[b] = min(dist[b], backup[a] + w);              // 进行松弛操作
        }
    }

    return dist[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);
        edges[i] = {a, b, w};
    }

    int t = bellman_ford();

    if (t > 0x3f3f3f3f / 2) puts("impossible");
    else printf("%d\n", t);

    return 0;
}