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

using namespace std;

const int N = 210, INF = 1e9;

int d[N][N];
int n, m, Q;

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 >> Q;
    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 -- )
    {
        int a, b, w;
        cin >> a >> b >> w;
        d[a][b] = min(d[a][b], w);
    }

    floyd();

    while ( Q -- )
    {
        int a, b;
        cin >> a >> b;
        if ( d[a][b] > INF / 2 ) puts("impossible");
        else cout << d[a][b] << endl;
    }

    return 0;
}