#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int BIG=1e9;
int n,m,Q,d[210][210],i,j,k;
void floyd()
{
    for(k=1;k<=n;k++)
        for(i=1;i<=n;i++)
            for(j=1;j<=n;j++)d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}
int main()
{
    int a,b,c;
    scanf("%d%d%d",&n,&m,&Q);
    for(i=1;i<=n;i++)
        for(j=1;j<=n;j++)
            if (i == j)d[i][j]=0;
            else d[i][j]=BIG;
    while(m--){
        scanf("%d%d%d",&a,&b,&c);
        d[a][b]=min(d[a][b],c);
    }
    floyd();
    while (Q--){
        scanf("%d%d",&a,&b);
        if(d[a][b]>BIG/2)puts("impossible");
        else printf("%d\n",d[a][b]);
    }
    return 0;
}