#include<bits/stdc++.h>

using namespace std;
const int inf=0x3f3f3f3f;
const int maxn=210;
int d[maxn][maxn],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){
                if(d[i][k]==inf||d[k][j]==inf)  continue;
                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)
            d[i][j]=(i==j)?0:inf;       //初始化
    for(int i=1;i<=m;++i){
        int a,b,c;
        scanf("%d %d %d",&a,&b,&c);
        d[a][b]=min(d[a][b],c);
    }
    Floyd();
    for(int i=1;i<=q;++i){
        int a,b;
        scanf("%d %d",&a,&b);
        if(d[a][b]==inf)    printf("impossible\n");
        else{
            printf("%d\n",d[a][b]);
        }
    }
}