#include <iostream>
using namespace std;

const int N = 210, M = 1e9 + 10;
int f[N][N];
int n, m, k;

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

int main() {
    cin >> n >> m >> k;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (i == j)
                f[i][j] = 0;
            else
                f[i][j] = M;
    while (m--) {
        int x, y, z;
        cin >> x >> y >> z;
        f[x][y] = min(f[x][y], z);
    }
    floyd();
    while (k--) {
        int x, y;
        cin >> x >> y;
        if (f[x][y] > M / 2)cout << "impossible\n";
        else cout << f[x][y] << '\n';
    }
    return 0;
}