#include<cstring>
#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() {
    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 printf("%d\n", d[a][b]);
    }

    return 0;
}