RT

#include<bits/stdc++.h>
using namespace std;
const int maxn=2e5+10;
struct edge{
	int to,v;
};
vector<edge> G[maxn];
int dis[3][maxn],n,m;
struct node{
	int pos,dis;
	friend bool operator <(node a,node b){
		return a.dis>b.dis;
	}
}tmp;
priority_queue<node> q;
void dij(){
	for(int i=1;i<=n;i++){
		dis[0][i]=dis[1][i]=0x7fffffff;
	}
	dis[0][1]=0;
	tmp={1,0};
	q.push(tmp);
	while(q.size()){
		tmp=q.top();
		q.pop();
		if(tmp.dis>dis[1][tmp.pos]){
			continue;
		}
		int u=tmp.pos,d=tmp.dis;
		for(int i=0;i<G[u].size();i++){
			int v=G[u][i].to,w=G[u][i].v;
			if(dis[0][v]>d+w){
				tmp.dis=dis[0][v]=d+w;
				tmp.pos=v;
				q.push(tmp);
			}
			if(dis[1][v]>d+w&&dis[0][v]<d+w){
				tmp.dis=dis[1][v]=d+w;
				tmp.pos=v;
				q.push(tmp);
			}
		}
	}
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		int u,v,w;
		cin>>u>>v>>w;
		G[u].push_back({v,w});
		G[v].push_back({u,w});
	}
	dij();
	cout<<dis[1][n];
	return 0;
}