#include <iostream>
#include <algorithm>

using namespace std;

const int N = 210, INF = 1e9;

int n, m, q;

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()
{
    scanf("%d%d%d", &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;
        scanf("%d%d%d", &a, &b, &w);
        d[a][b] = min(d[a][b], w);
    }
    floyd();
    while(q --)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        if(d[a][b] > INF / 2) cout << "impossible" << endl;
        else printf("%d\n", d[a][b]);
    }
    return 0;
}