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

using namespace std;

const int N = 510, M = 10010;

// 邻接表存储方式2(n, m)
int n, m, k;
struct Edge
{
    int a, b, c;
}edges[M];


int dist[N];
int last[N];

void bellman_ford()
{
    // Bellman_Ford算法最短路：源，距，更新
    int goal = 1;

    // int dist[N];
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;

    for (int i = 0; i < k; i ++ )
    {
        // Bellman_Ford：严格控制迭代轮数
        memcpy(last, dist, sizeof dist);
        for (int j = 0; j < m; j ++ )
        {
            // Bellman_Ford更新公式：类似于宽搜策略
            // 松弛搜索：a->b, b->c, 第一轮(a只能到b, b->c不更新), 第二轮(a->c的路径自动更新)
            auto e = edges[j];
            dist[e.b] = min(dist[e.b], last[e.a] + e.c);
        }
    }
}

int main()
{
    scanf("%d%d%d", &n, &m, &k);

    for (int i = 0; i < m; i ++ )
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        edges[i] = {a, b, c};
    }

    bellman_ford();

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

    return 0;
}