#include <iostream>
#include <cstring>

using namespace std;

const int N = 210;

int g[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 ++ )
            {
                g[i][j] = min(g[i][j], g[i][k] + g[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) g[i][j] = 0;
            else g[i][j] = 0x3f3f3f3f;
        }

    for (int i = 0; i < m; i ++ )
    {
        int x, y, z;
        cin >> x >> y >> z;
        g[x][y] = min(g[x][y], z);
    }

    floyd();

    while (k -- )
    {
        int a, b;
        cin >> a >> b;
        if (g[a][b] > 0x3f3f3f3f / 2) puts("impossible");
        else cout << g[a][b] << endl;
    }

    return 0;
}