import java.util.*;

public class Main{
    static int N = 510;
    static int n,m,k;
    static int[][] dist = new int[N][N];
    static void floyd(){
        for(int k=1;k<=n;k++){
            for(int i=1;i<=n;i++){
                for(int j=1;j<=n;j++){
                    dist[i][j]=Math.min(dist[i][j],dist[i][k]+dist[k][j]);
                }
            }
        }
    }

    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        m = sc.nextInt();
        k = sc.nextInt();
        for(int i=0;i<N;i++){
            for(int j=0;j<N;j++){
                if(i==j)    dist[i][j]=0;
                else    dist[i][j]=0x3f3f3f;
            }
        }
        while(m-->0){
            int x = sc.nextInt();
            int y = sc.nextInt();
            int z = sc.nextInt();
            dist[x][y] = Math.min(dist[x][y], z);
        }
        floyd();
        while(k-->0){
            int x = sc.nextInt();
            int y = sc.nextInt();
            if(dist[x][y]>0x3f3f3f/2)    System.out.println("impossible");
            else    System.out.println(dist[x][y]);
        }
    }
}