#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll N = 300009;
vector<pair<ll, pair<ll, ll > > > v[N];
ll d1[N],dn[N], f[N], g[N],ea[N],eb[N],ec[N];
multiset<pair<ll,ll> > S;
void ad(ll x){
g[x] = 1;
for(auto E : v[x]){
ll y = E.first, l = E.second.first, u= E.second.second;
if(g[y] == 1) S.erase(S.find({d1[y] + l + dn[x], u}));
else S.insert({d1[x] + l + dn[y], u});
}
}
ll A = 0;
main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
ll n, m;
cin >> n >> m;
for(ll i = 0; i < m; i++){
cin>>ea[i]>>eb[i]>>ec[i];
}
for(ll i = m-1; i >= 0; i--){
ll a = ea[i], b = eb[i], c = ec[i];
v[a].push_back({b, {c,A}});
v[b].push_back({a, {c,A}});
A = max(A, c);
}
for(ll i = 1; i <= n; i++){
d1[i] = 1e18;
dn[i] = 1e18;
}
d1[1] = 0;
dn[n] = 0;
priority_queue<pair<ll, ll> > q;
q.push({0, 1});
while(q.size()){
ll x = q.top().second;
q.pop();
if(f[x]) continue;
f[x] = 1;
for(auto E: v[x]){
ll y = E.first, l = E.second.first;
if(!f[y] && d1[y] > d1[x] + l){
d1[y] = d1[x] + l;
q.push({-d1[y], y});
}
}
}
q.push({0, n});
for(ll i = 1; i <= n; i++)
f[i] = 0;
while(q.size()){
ll x = q.top().second;
q.pop();
if(f[x]) continue;
f[x] = 1;
for(auto E: v[x]){
ll y = E.first, l = E.second.first;
if(!f[y] && dn[y] > dn[x] + l){
dn[y] = dn[x] + l;
q.push({-dn[y], y});
}
}
}
vector<pair<ll,ll> > W;
ll ans = d1[n];
for(ll i = 1; i <= n; i++){
W.push_back({d1[i], i});
}
sort(W.begin(), W.end());
for(ll i = 0; i < n; i++){
ll x = W[i].second;
if(x == n) break;
ad(x);
ll U = S.begin()->first + S.begin()->second;
auto it = S.begin();
it++;
if(it != S.end()) U = min(U, it->first);
ans = max(ans, U);
}
cout<<ans<<endl;
}
