using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
using System.Threading;
using System.Runtime.CompilerServices;
static class Program{
	const int mod=(int)1e9+7;
	const long inf=long.MaxValue/3;
	static List<ValueTuple<int,int>>[] li;
	static bool[] b;
	static void Main(){
		Sc sc=new Sc();
		var s=sc.Ia;
		int n=s[0],m=s[1];
		li=new List<ValueTuple<int,int>>[n+1];
		b=new bool[n+1];
		var c=new long[n+1];
		var h=new int[n+1];
		for(int i=1;i<=n;i++){
			li[i]=new List<ValueTuple<int,int>>();
			c[i]=inf;
		}
		var g=new int[m][];
		for(int i=0;i<m;i++){
			g[i]=sc.Ia;
			li[g[i][0]].Add(ValueTuple.Create(g[i][1],i));
			li[g[i][1]].Add(ValueTuple.Create(g[i][0],i));
		}
		var pq=new Rheap<(int,int)>(32);
		pq.Push(new Rheap<(int,int)>.Dt(0,(1,-1)));
		c[1]=0;
		while(pq.cnt>0){
			var e=pq.Dequeue;
			if(b[e.d.Item1]){continue;}
			b[e.d.Item1]=true;
			h[e.d.Item1]=e.d.Item2;
			if(e.d.Item1==n){break;}
			for(int i=0;i<li[e.d.Item1].Count;i++){
				if(!b[li[e.d.Item1][i].Item1]&&c[li[e.d.Item1][i].Item1]>g[li[e.d.Item1][i].Item2][2]+e.n){
					pq.Push(new Rheap<(int,int)>.Dt(g[li[e.d.Item1][i].Item2][2]+e.n,(li[e.d.Item1][i].Item1,li[e.d.Item1][i].Item2)));
					c[li[e.d.Item1][i].Item1]=g[li[e.d.Item1][i].Item2][2]+e.n;
				}
			}
		}
		var p=n;
		long ans=c[n];
		while(h[p]!=-1){
			(g[h[p]][2],g[h[p]][3])=(g[h[p]][3],g[h[p]][2]);
			p=p==g[h[p]][0]?g[h[p]][1]:g[h[p]][0];
		}
		c=Enumerable.Repeat(inf,n+1).ToArray();
		b=new bool[n+1];
		pq=new Rheap<(int,int)>(32);
		pq.Push(new Rheap<(int,int)>.Dt(0,(1,-1)));
		c[1]=0;
		while(pq.cnt>0){
			var e=pq.Dequeue;
			if(b[e.d.Item1]){continue;}
			b[e.d.Item1]=true;
			if(e.d.Item1==n){break;}
			for(int i=0;i<li[e.d.Item1].Count;i++){
				if(!b[li[e.d.Item1][i].Item1]&&c[li[e.d.Item1][i].Item1]>g[li[e.d.Item1][i].Item2][2]+e.n){
					pq.Push(new Rheap<(int,int)>.Dt(g[li[e.d.Item1][i].Item2][2]+e.n,(li[e.d.Item1][i].Item1,li[e.d.Item1][i].Item2)));
					c[li[e.d.Item1][i].Item1]=g[li[e.d.Item1][i].Item2][2]+e.n;
				}
			}
		}
		Console.WriteLine("{0}",ans+c[n]);
	}
}
public class Rheap<T>{
	public class Dt{
		public long n;
		public T d;
		public Dt(long n,T d){this.n=n;this.d=d;}
		public override string ToString()=>"d:"+d.ToString()+" n:"+n.ToString();
	}
	private const int m=65;
	private long la=0;
	private Dt[][] bf;
	private int[] h;
	public int cnt=0;
	public Rheap(int max){
		bf=new Dt[m][];
		h=new int[m];
		for(int i = 0;i<m;i++) {bf[i]=new Dt[max];}
	}
	public void Push(Dt x){
		int a=x.n!=la?Bsr(la^x.n)+1:0;
		if(h[a]==bf[a].Length){Extend(a);}
		bf[a][h[a]]=x;
		cnt++;
		h[a]++;
	}
	public Dt Peek{get{
		if(h[0]==0){
			for(int i = 1;i<m;i++) {
				if(h[i]>0){
					int p=0;
					for(int j = 1;j<h[i];j++) {
						if(bf[i][p].n>bf[i][j].n){p=j;}
					}
					la=bf[i][p].n;
					for(int j = 0;j<h[i];j++) {
						Push(bf[i][j]);
						cnt--;
					}
					h[i]=0;
					break;
				}
			}
		}
		return bf[0][h[0]-1];
	}}
	public Dt Dequeue{get{
		var e=Peek;
		h[0]--;
		cnt--;
		return e;
	}}
	private void Extend(int n){
		var nhe=new Dt[bf[n].Length<<1];
		Array.Copy(bf[n],nhe,bf[n].Length);
		bf[n]=nhe;
	}
	private int Bsr(long b){
		int n=0;
		if(b==0){return -1;}
		if((b&-4294967296)!=0){b=b&-4294967296;n+=32;}
		if((b&-281470681808896)!=0){b=b&-281470681808896;n+=16;}
		if((b&-71777214294589696)!=0){b=b&-71777214294589696;n+=8;}
		if((b&-1085102592571150096)!=0){b=b&-1085102592571150096;n+=4;}
		if((b&-3689348814741910324)!=0){b=b&-3689348814741910324;n+=2;}
		if((b&-6148914691236517206)!=0){b=b&-6148914691236517206;n+=1;}
		return n;
	}
}
public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),long.Parse);}
	public double[] Da2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),double.Parse);}}
	public double[] Da3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),double.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}