import java.util.*;

public class Main{
    static int N = 510,M = 100010;
    static int n,m,k;
    static int[] dist = new int[N],back = new int[N];
    static Node[] node = new Node[M];
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        m = sc.nextInt();
        k = sc.nextInt();
        Arrays.fill(dist,0x3f3f3f3f);
        for(int i = 0;i < m;i++){
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
              node[i] = new Node(a,b,c);
        }
        bellman_ford();

    }
    static void bellman_ford(){
        dist[1] = 0;
        for(int i = 0;i < k;i++){
        back = Arrays.copyOf(dist,n + 1);
        for(int j = 0;j < m;j++){
            Node no = node[j];
            int a = no.a;
            int b = no.b;
            int c = no.c;
            dist[b] = Math.min(back[a] + c,dist[b]);
        }
        }
        if(dist[n] > 0x3f3f3f3f/2){
            System.out.print("impossible");
        }else{
            System.out.print(dist[n]);
        }
    }
   static class  Node{
        int a,b,c;
        public Node(int a,int b,int c){
            this.a = a;
            this.b = b;
            this.c = c;
        }
    } 
}