/*
I:(n,m)有向图;
(n,m)有向图，可能重边、自环，边权可能为负；
k个询问，x,y之间的最短距离，若不存在则输出“impossible”
O:每个询问的最小路径长度，不存在则输出“impossible”;

I:
3 3 2
1 2 1
2 3 2
1 3 1
2 1
1 3
O:
impossible
1
*/

#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 210, INF = 1e9;

int n, m, Q;
int d[N][N];

// floyd算法：将图邻接矩阵g[][]转化为最短距离矩阵d[][]
void floyd()
{
    // floyd算法需要邻接矩阵特殊初始化：有权(自己到自己是默认有权)，或者INF

    // 经过k:1~n次迭代，更新路径
    // BFS思路可以理解此算法的有效性：初始还不能被更新到，迭代轮数达到后就自然而然更新到
    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()
{
    scanf("%d%d%d", &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, c;
        scanf("%d%d%d", &a, &b, &c);
        d[a][b] = min(d[a][b], c);
    }

    floyd();

    while (Q -- )
    {
        int a, b;
        scanf("%d%d", &a, &b);

        int t = d[a][b];
        if (t > INF / 2) puts("impossible");
        else printf("%d\n", t);
    }

    return 0;
}