floyd
#include<bits/stdc++.h>
using namespace std;
const int N = 202, INF = 0x3f3f3f3f;
int n, m, q;
int g[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 ++ )
g[i][j] = min(g[i][j], g[i][k] + g[k][j]);
}
int main()
{
cin >> n >> m >> q;
for(int i = 0; i <= n; i ++ )
for(int j = 0; j <= n; j ++ )
if(i == j) g[i][j] = 0;
else g[i][j] = INF;
while(m -- )
{
int f, t, l;
cin >> f >> t >> l;
g[f][t] = min(g[f][t], l);
}
floyd();
while(q -- )
{
int f, t;
cin >> f >> t;
if(g[f][t] > INF / 2) puts("impossible");
else cout << g[f][t] << endl;
}
return 0;
}