#include <iostream>
#include <cstring>

using namespace std;

const int N = 510, M = 10010;

int n, m, k;
int dist[N], backup[N]; //backup[N]为回溯数组，记录上一次的结果

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

void 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 = 1; j <= m; j ++ ) //松弛操作
        {
            int a = edge[j].a, b = edge[j].b, w = edge[j].w;
            dist[b] = min(dist[b], backup[a] + w);
        }
    }
}

int main()
{
    cin >> n >> m >> k;
    for(int i = 1; i <= m; i ++ )
    {
        int a, b, w;
        cin >> a >> b >> w;
        edge[i] = {a, b, w};
    }

    bellman_ford();

    if(dist[n] > 0x3f3f3f3f / 2) cout << "impossible" << endl;
    else cout << dist[n] << endl;
    return 0;
}