#include<bits/stdc++.h>
using namespace std;

const int N = 210;
const int INF = 0x3f3f3f3f; 
int n,m,k,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;
    memset(d, INF, sizeof d);
    for(int i = 1; i <= n; i++) d[i][i] = 0;

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

    floyd();

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

    return 0;
}