#include<bits/stdc++.h>
using namespace std;
#define int long long

int n,r;
int h[5005],to[10005],ne[10005],w[10005],idx;
bool vis[5005];
int g[5005],dis[5005];
int k;
priority_queue<pair<int,int>,vector<pair<int,int> >,greater<pair<int,int> > >heap;

struct node
{
	int step,x;
	bool operator<(node y)const
	{
		return this->step+dis[this->x]>y.step+dis[y.x];
	}
};

priority_queue<node>q;

void add(int x,int y,int z)
{
	to[idx]=y;
	w[idx]=z;
	ne[idx]=h[x];
	h[x]=idx++;
}

void DijkstraPhoenix(void)
{
	dis[n]=0;
	heap.push(make_pair(dis[n],n));
	while(!heap.empty())
	{
		int y=heap.top().second;
		heap.pop();
		if(vis[y])continue;
		vis[y]=true;
		for(int i=h[y];i!=-1;i=ne[i])
		{
			int z=to[i];
			if(dis[y]+w[i]<dis[z])
			{
				dis[z]=dis[y]+w[i];
				heap.push(make_pair(dis[z],z));
			}
		}
	}
}

void Astar(void)
{
	q.push(node{0,1});
	while(!q.empty())
	{
		node x=q.top();
		q.pop();
		int f=x.step,s=x.x;
		if(s==n)
		{
			if(k==1)
			{
				cout<<f;
				exit(0);
			}
			else k++;
		}
		for(int i=h[s];i!=-1;i=ne[i])
		{
			int j=to[i];
			
			q.push(node{f+w[i],j});
		}
	}
}

signed main(void)
{
	memset(h,-1,sizeof(h));
	memset(dis,0x3f,sizeof(dis));
	memset(vis,false,sizeof(vis));
	
	cin>>n>>r;
	for(int i=1;i<=r;i++)
	{
		int u,v,e;
		cin>>u>>v>>e;
		add(u,v,e);
		add(v,u,e);
	}
	
	DijkstraPhoenix();
	Astar();
	return 0;
}