#include <iostream>
#include <cstdio>

using namespace std;
const int N = 210;


int INF = 1E9, n, m, q;
int dis[N][N];

int Floyd() {
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            for (int k = 1; k <= n; k++) {
                dis[j][k] = min(dis[j][k], dis[j][i] + dis[i][k]);
            }
}

int main() {
    cin >> n >> m >> q;

    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (i == j) dis[i][j] = 0;
            else dis[i][j] = INF;

    while (m--) {
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);
        dis[a][b] = min(dis[a][b], c);
    }

    Floyd();

    while (q--) {
        int a, b;
        scanf("%d %d", &a, &b);
        if (dis[a][b] > INF / 2) cout << "impossible" << endl;
        else cout << dis[a][b] << endl;
    }


    return 0;
}