#include<bits/stdc++.h>
#define IOS ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define debug(x) (cout<<(#x)<<':'<<(x)<<'\n')
#define endl '\n' 
#define lowbit(x) x & (-x)
#define mst(a) memset(a,0,sizeof a)
#define y second
#define x first
using namespace std;
typedef long long ll; typedef pair<int,int> PII; typedef unsigned long long ull;
const int N = 3e5+10,P = 131,INF = 0x3f3f3f3f;
vector<PII> ver[N];
PII ans[N];
bool st[N];
int res[N];
void insert(int idx,int idx_,int v){
    vector<int> t={v,ans[idx_].first,ans[idx_].second};
    sort(t.begin(),t.end());
    ans[idx]={t[2],t[1]};
}
int sum(PII a){
    return a.first+a.second;
}
void bfs(){
    queue<int> q;
    q.push(1);
    while(q.size()){
        int u = q.front();
        //cout<<u<<" "<<ans[u].first<<" "<<ans[u].second<<" "<<endl;
        st[u]=false;
        q.pop();
        for(PII it:ver[u]){
            //cout<<u<<endl;
            int v=it.first,val=it.second;
            PII pre = ans[v];
            insert(v,u,val);
            PII cur = ans[v];
            if(res[v]==INF || cur.second==0 || (sum(cur)<sum(pre))){
                if(!st[v]) st[v]=true,q.push(v);
                res[v]=min(res[v],sum(cur));
            }else ans[v]=pre;
        }
    }
}
void solve(){
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++) res[i]=0x3f3f3f3f;
    while(m--){
        int a,b,c;
        cin>>a>>b>>c;
        ver[a].push_back({b,c});
        ver[b].push_back({a,c});
    }
    bfs();
    cout<<res[n]<<"\n";
}
int main(){
    IOS;
    int T = 1;
    //cin>>T;
    while(T--) solve();
    return 0;
}