import java.util.*;
public class BellmanFord {
  static boolean debug = false;
  static class Edge {
    int from, to, cost;
    public Edge(int from,int to,int cost) {
      this.from = from; this.to = to; this.cost = cost;
    }
    public String toString() { return "edge["+from+", "+to+", "+cost+"]"; }
  }
  int MAX_V;
  ArrayList<Edge> edges;
  int[] distance;
  public BellmanFord(int n,int m) {
    MAX_V = n;
    edges = new ArrayList<Edge>();
    distance = new int[n];
  }
  public void addEdge(int from, int to, int cost) {
    edges.add(new Edge(from,to,cost));
  }
  public void shortestPath(int src, int dst) {
    for (int i=0; i<distance.length; i++) distance[i] = Integer.MAX_VALUE;
    distance[src] = 0;
    int count = 0;
    boolean updated = true;
    while (updated) {
      updated = false;
      for (Edge e: edges) {
        if (distance[e.from] != Integer.MAX_VALUE
	    && distance[e.to] > distance[e.from] + e.cost) {
          distance[e.to] = distance[e.from] + e.cost;
          updated = true;
          if (count == MAX_V-1) throw new RuntimeException("negative loop");
        }
      }
      count ++;
    }
  }
  public static void main(String[] args) {
    for (int i=0; i<args.length; i++) {
      if (args[i].equals("-d")) debug = !debug;
    }
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt(), m = sc.nextInt();
    BellmanFord bf = new BellmanFord(n, m);
    for (int i=0; i<m; i++) {
      int from = sc.nextInt(), to = sc.nextInt(), cost = sc.nextInt();
      bf.addEdge(from,to,cost);
    }
    int src = sc.nextInt(), dst = sc.nextInt();
    try {
	bf.shortestPath(src,dst);
	System.out.println(bf.distance[dst]);
    } catch (Exception e) {
	System.out.println("negative loop");
    }
    if (debug) {
      for (int i=0; i<bf.MAX_V; i++) System.out.print(bf.distance[i]+" ");
      System.out.println();
    }
  }
}