import java.util.*;
public class POJ2387 {
	public static class Pair implements Comparable<Pair>
	{
		int v,w;
		Pair(int v,int weight)
		{
			this.v=v;w=weight;
		}
		public int compareTo(Pair x) {
			return this.w-x.w;
		}
	}

	public static void main(String[] args) {
		Scanner in=new Scanner(System.in);
		int t=in.nextInt(),n=in.nextInt();
		ArrayList<Pair>[] path=new ArrayList[n+1];
		int[] d=new int[n+1];
		for(int i=1;i<=n;i++)
		{
			path[i]=new ArrayList<Pair>();
			d[i]=-1;
		}
		for(int i=0;i<t;i++)
		{
			int a=in.nextInt(),b=in.nextInt(),
				c=in.nextInt();
			path[a].add(new Pair(b,c));
			path[b].add(new Pair(a,c));
		}
		Queue<Pair> q=new PriorityQueue<Pair>();
		d[1]=0;q.add(new Pair(1,0));
		while(!q.isEmpty())
		{
			Pair a=q.poll();
			while(!q.isEmpty()&&a.w>d[a.v])
				a=q.poll();
			for(int i=0;i<path[a.v].size();i++)
			{
				Pair b=path[a.v].get(i);
				if(d[b.v]==-1||d[b.v]>d[a.v]+b.w)
				{
					d[b.v]=d[a.v]+b.w;
					q.add(new Pair(b.v,d[b.v]));
				}
			}
		}
		System.out.println(d[n]);
	}
}