//Think twice,code once.
#include<bits/stdc++.h>
#define endl '\n'
#define INF 0x3f3f3f3f3f3f3f
#define inf 0x3f3f3f3f
#define ff first
#define ss second
#define pii pair<int,int>
#define int long long
#define mem(i,n) memset(i,n,sizeof i)
#define dg(a) std::cout << #a << " = " << a << endl
typedef long long ll;
typedef unsigned long long ull;
using namespace std;

const int N=3e5+10;

struct node
{
    int u;
    int val=INF;
    int m1=0,m2=0;
    operator< (const node&b) const {
        if(val!=b.val) return val>b.val;
        else m1>b.m1;
    }
};

vector<pii>g[N];
node dis[N];
bool vis[N];

void dij()
{
    dis[1]={1,0,0,0};
    priority_queue<node>q;
    q.push(dis[1]);
    while(q.size())
    {
        auto u=q.top().u;
        q.pop();
        if(vis[u]) continue;
        vis[u]=1;
        for(auto [v,w]:g[u])
        {
            node nu=dis[u];
            nu.u=v;
            if(w>nu.m2) nu.m2=w;
            if(nu.m2>nu.m1) swap(nu.m2,nu.m1);
            nu.val=nu.m1+nu.m2;
            if(nu.val<=dis[v].val)
            {
                dis[v]=nu;
                q.push(dis[v]);
            }
        }
    }
}

void solve()
{
    int n,m;
    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[n].val << endl;
}

int32_t main()
{
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);
    int t = 1;
    // std::cin >> t;
    while(t--) solve();
    return 0;
}

answer.code:23:5: error: ISO C++ forbids declaration of ‘operator<’ with no type [-fpermissive]
   23 |     operator< (const node&b) const {
      |     ^~~~~~~~
answer.code: In member function ‘int node::operator<(const node&) const’:
answer.code:26:5: warning: control reaches end of non-void function [-Wreturn-type]
   26 |     }
      |     ^