#include<iostream>
using namespace std;

const int N = 210, INF = 1e9;

int n, m, k, x, y, z;
int d[N][N];

void floyd() {
    for (int k = 1; k <= n; k ++ ) {
        for (int i = 1; i <= n; i ++ ) {
            for (int j = 1; j <= n; j ++ ) d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
        }
    }
}

int main() {
    cin >> n >> m >> k;
    for (int i = 1; i <= n; i ++ ) {
        for (int j = 1; j <= n; j ++ ) {
            if (i == j) d[i][j] = 0;
            else d[i][j] = INF;
        }
    }

    while (m -- ) {
        cin >> x >> y >> z;
        d[x][y] = min(d[x][y], z);
    }

    floyd();

    while (k -- ) {
        cin >> x >> y;
        if (d[x][y] > INF / 2) puts("impossible");
        else cout << d[x][y] << endl;
    }

    return 0;
}