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

using namespace std;

const int N = 1e6 + 10;
int h[N], e[N], ne[N], idx;
int w[N];
int n, m, k;
int dist[N];
int last[N];
void add(int a, int b, int c) {

    e[idx] = b, ne[idx] = h[a], w[idx] = c;
    h[a] = idx++;

}
void bellman_ford()
{
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;

    for (int i = 0; i < k; i++) {

        memcpy(last, dist, sizeof dist);
        for (int j = 1; j <= n; j++)
            for (int t = h[j]; ~t; t = ne[t]) {

            int k = e[t];
            dist[k] = min(dist[k], last[j] + w[t]);
            //cout << dist[j] << ' ';
        }

    }

}
int main() {

    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> n >> m;
    cin >> k;
    memset(h, -1, sizeof h);
    for (int i = 0; i < m; i++)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);

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