#include <bits/stdc++.h>
#define dd(x) cout << #x << "\n"
#define d(x) cout << #x  << ": " << x << "\n"
#define SZ(x) ((int)(x).size())
using namespace std;
#define int long long
using pii = pair<int, int>;
using vpii = vector<pii>;
using vi = vector<int>;
using vii = vector<vector<int>>;
using a3 = array<int, 3>;
using ll = long long;
const int inf = 0x3f3f3f3f3f3f3f3fLL;

// #define MULTI_TEST
const int N = 3e5 + 5;
vpii adj[N];

void solve() {
    int n, m; cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }

    vector<int> vis(n + 1);
    vpii dis(n + 1);
	fill(dis.begin(), dis.end(), pair(inf, inf));

    priority_queue<
        array<int, 3>,
        vector<array<int, 3>>,
        greater<array<int, 3>>
    > Q;

    dis[1] = {inf, inf}; Q.push({inf, inf, 1});

    while(!Q.empty()) {
        auto [d1, d2, u] = Q.top(); Q.pop();
		if(vis[u]) continue; 
		vis[u] = 1;

		for(auto [v, w] : adj[u]) {
            vi tt{d1, d2, w};
            sort(tt.begin(), tt.end());
            while(tt.back() == inf) tt.pop_back();
            reverse(tt.begin(), tt.end());

            pii newdis = {tt[0], inf};
            if(tt.size() > 1) newdis.second = tt[1];

			if(newdis < dis[v]) {
				dis[v] = newdis;
				Q.push({dis[v].first, dis[v].second, v});
			}
		}
	}

    int ans = 0;
    if(dis[n].first != inf) ans += dis[n].first;
    else if(dis[n].second != inf) ans += dis[n].second;
    
    cout << dis[n].first + dis[n].second << "\n";
}

signed main() {
    ios::sync_with_stdio(false); cin.tie(0);
#ifdef MULTI_TEST
    int T; cin >> T;
#else
    int T = 1;
#endif
    while(T--) solve();
    return 0;
}