#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define int long long
using namespace std;
const int N=1e6+10;
int n,m;
struct node{
    int to,nxt,w;
}e[N*2];
int head[N],tot;
void add(int a,int b,int c){
    e[++tot].nxt=head[a];
    head[a]=tot;
    e[tot].to=b;
    e[tot].w=c;
}
int ans[N];
struct Node{
    int id;
    int ans1,ans2;
    bool operator <(const Node &p)const{
        return p.ans1+p.ans2<ans1+ans2;
    }
};
int vis[N];
priority_queue<Node>q;
void dij(){
    for(int i=1;i<=n;i++){
        ans[i]=LONG_LONG_MAX;vis[i]=0;
    }
    ans[1]=0;
    q.push({1,0,0});
    while(!q.empty()){
        Node t=q.top();q.pop();
        int u=t.id;
        if(vis[u])continue;
        vis[u]=1;
        for(int i=head[u];i;i=e[i].nxt){
            int v=e[i].to;
            if(vis[v])continue;
            int anss1=-1,anss2=-1;
            if(e[i].w>t.ans1){
                anss2=t.ans1;
                anss1=e[i].w;
            }
            else if(e[i].w>t.ans2){
                anss1=t.ans1;
                anss2=e[i].w;
            }
            if(anss1==-1)anss1=t.ans1;
            if(anss2==-1)anss2=t.ans2;
            if(anss1+anss2<ans[v]){
                ans[v]=anss1+anss2;
            //    cout<<v<<" "<<anss1<<"-="<<anss2<<"\n";
                if(!vis[v]){
                    q.push({v,anss1,anss2});
                }
            }
        }
    }
}
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin>>n>>m;
    int u,v,w;
    int ww=1e9+10;
    for(int i=1;i<=m;i++){
        cin>>u>>v>>w;
        if(u==1&&v==n)ww=min(ww,w);
        if(u==n&&v==1)ww=min(ww,w);
        add(u,v,w);
        add(v,u,w);
    }
    dij();
    cout<<min(ans[n],ww);
    return 0;
}

answer.code: In function ‘void dij()’:
answer.code:32:16: error: ‘LONG_LONG_MAX’ was not declared in this scope
   32 |         ans[i]=LONG_LONG_MAX;vis[i]=0;
      |                ^~~~~~~~~~~~~