一、Edge边表示、判断负环

       注意这里的图一般用有向图表示 也就是说 1 – 2， 2 – 1 如果权重为负值  那么 也算有负权环（这里表示了添加两条边的方法）

       这里因为添加双向边 则 一旦有负w出现就会认为是负权环

import java.util.Scanner;

public class Main {
	static Edge []edges;
	static boolean []visit;
	static int n, m;
	static int tol;
	static int[]dis;
	static int INF = 9999999;
	static int[]head;
	static boolean hasNegCycle = false;
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNext()) {
			n = in.nextInt();
			m = in.nextInt();
			if(n == 0 && m == 0)
				break;
			edges = new Edge[2*m+1];
			for(int i = 1; i <= 2*m; i++ )
				edges[i] = new Edge();
			tol = 1;
			head = new int[n+1];
			dis = new int[n+1];
			for(int i = 1; i <= n; i++ )
				head[i] = -1;
			for(int i = 1; i <= m; i++ ) {
				int u = in.nextInt();
				int v = in.nextInt();
				int w = in.nextInt();
				add(u, v, w);
				add(v, u, w);
			}
			bell_man();
			if(!hasNegCycle) {
				System.out.println(dis[n]);
			}
			else
				System.out.println("hasNegtiveCycle");
//			for(int i = 1; i < tol; i++ ) {
//				Edge e = edges[i];
//				System.out.println(e.from + " " + e.to + " " + e.w);
//			}
		}
		
	}
	public static void bell_man() {
		
		for(int i = 1; i <= n; i++ ) {
			dis[i] = (i == 1) ? 0 : INF;
		}
		
		for(int i = 1; i < n; i++ ) {
			int flag = 0;
			for(int j = 1; j <= 2*m; j++ ) {
				Edge e = edges[j];
				if(dis[e.to] > dis[e.from] + e.w) {
					flag = 1;
					dis[e.to] = dis[e.from] + e.w;
				}
			}
			if(flag == 0)
				break;
		}
		hasNegCycle = false;
		for(int i = 1; i <= 2*m; i++ ) {
			Edge e = edges[i];
			if(dis[e.to] > dis[e.from] + e.w) {
				hasNegCycle = true;
				break;
			}
		}
	}
	public static void add(int from, int to, int w) {
		edges[tol].from = from;
		edges[tol].to = to;
		edges[tol].w = w;
		edges[tol].next = head[from];
		head[from] = tol++;
	}

}

class Edge{
	int from, to;
	int w;
	int next;
//	public Edge(int from, int to) {
//		this.from = from;
//		this.to = to;
//		this.w = w;
//	}
}