import java.io.*;
import java.util.Arrays;

class Main {

    static final int INF = 0x3fffffff;

    //邻接矩阵存储
    //Floyd算法只需开一个邻接矩阵，原地操作
    static int[][] g = new int[210][210];

    static {
        for (int i = 0; i < 210; i++) {
            Arrays.fill(g[i], INF);
        }
    }

    static int n, m, k;

    static void insert(int a, int b, int v) {
        g[a][b] = Math.min(g[a][b], v);
    }

    static 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] = Math.min(g[i][j], g[i][k] + g[k][j]);
    }

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(isr);
        String[] strs = in.readLine().split(" ");
        n = Integer.parseInt(strs[0]);
        m = Integer.parseInt(strs[1]);
        k = Integer.parseInt(strs[2]);
        for (int i = 1; i <= n; i++) g[i][i] = 0;
        for (int i = 0; i < m; i++) {
            strs = in.readLine().split(" ");
            int a = Integer.parseInt(strs[0]);
            int b = Integer.parseInt(strs[1]);
            int v = Integer.parseInt(strs[2]);
            insert(a, b, v);
        }
        OutputStreamWriter osw = new OutputStreamWriter(System.out);
        BufferedWriter out = new BufferedWriter(osw);

        floyd();
        for (int i = 0; i < k; i++) {
            strs = in.readLine().split(" ");
            int a = Integer.parseInt(strs[0]);
            int b = Integer.parseInt(strs[1]);
            if (g[a][b] > INF / 2) out.write("impossible\n");
            else out.write(g[a][b] + "\n");
        }

        in.close();
        isr.close();
        out.flush();
        out.close();
        osw.close();
    }
}