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

const int MAX = 3e5 + 9;
struct edge{
	int u, v, w;
};

struct node{
	int u, w1, w2;
	friend bool operator < (node a, node b)
	{
		return a.w1 + a.w2 > b.w1 + b.w2;
	}
};

int n, m;
bool vis[MAX];
vector<edge> g[MAX];
priority_queue<node> q; 

void dijk()
{
	q.push({1, 0, 0});
	int flag = 1e9 + 7;
	while (!q.empty())
	{
		int u = q.top().u;
		int w1 = q.top().w1;
		int w2 = q.top().w2;
//		cout << u << " " << w1 << " " << w2 << "\n";
		if (u == n)
		{
			flag = min(flag, w1 + w2);
		}
		q.pop();
		if (vis[u]) continue;
		vis[u] = 1;
		for (int k = 0; k < g[u].size(); k++)
		{
			node nnn;
			int v = g[u][k].v;
			int w = g[u][k].w;
			if (w <= min(w1, w2))
			{
				nnn.u = v;
				nnn.w1 = w1;
				nnn.w2 = w2;
			}
			else
			{
				nnn.u = v;
				nnn.w1 = max(w1, w2);
				nnn.w2 = w;
			}
			q.push(nnn);
		}
	}
	cout << flag << "\n";
}



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