#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

struct edge{
    ll p;//点
    ll w;//辺の重み*-1
};
vector<vector<edge> > graph(100000);
vector<ll> dis(100000);
ll v,e,r;//vは頂点,eは辺,rは始点
void dijkstra(){
  for(int i = 0;i < v;i++)dis[i] = pow(10,18);
    dis[r] = 0;
    priority_queue<pair<ll,ll> > que;//重み、頂点
    que.push(make_pair(0,r));
    while(!que.empty()){
        edge now;
        now.p = que.top().second;
        now.w = que.top().first * -1;
        que.pop();
        if(dis[now.p] < now.w)continue;
        for(int i = 0;i < (int)graph[now.p].size();i++){
            if(dis[graph[now.p][i].p] > now.w + graph[now.p][i].w){
                dis[graph[now.p][i].p] = now.w + graph[now.p][i].w;
                que.push(make_pair(dis[graph[now.p][i].p] * -1,graph[now.p][i].p));
            }
        }
    }
}


int main(){
    cin >> v >> e;
    for(int i = 0;i < e;i++){
        ll a,b,c;
        cin >> a >> b >> c;
        a--,b--;
        edge ma = {b,c};
        edge mb = {a,c};
        graph[a].push_back(ma);
        graph[b].push_back(mb);
    }
    r = 0;
    dijkstra();
    cout << dis[v - 1] * 2 << endl;
}