#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdio>
using namespace std;
const int N = 210;
const int INF = 1000000;
int dist[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++)
                dist[i][j]=min(dist[i][j],dist[i][k]+dist[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) dist[i][j]=0;
            else dist[i][j]=INF;
        }
    }
    while (m--)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        dist[a][b]=min(dist[a][b],c);
    }
    floyd();

    while (q--)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        if (dist[x][y]>INF/2) puts("impossible");
        else printf("%d\n",dist[x][y]);
    }
    return 0;
}