#include <bits/stdc++.h>
using namespace std;
#define int long long
const int INF = (int)1e18;
int ferries(int n , int m , vector<int> a , vector<int> b , vector<int> c) {
vector<vector<pair<int , int>>> adj(n);
for (int i = 0 ; i < m ; i++) {
a[i] -= 1 , b[i] -= 1;
adj[a[i]].emplace_back(b[i] , c[i]);
}
vector<int> dp(n , -1) , vis(n);
function<long long(int)> Solve = [&](int node) -> long long {
if (node == n - 1) {
return 0;
}
if (vis[node] == 1) {
return -1;
}
if (dp[node] != -1) {
return dp[node];
}
vis[node] = 1;
vector<int> d , s;
for (auto x : adj[node]) {
int g = Solve(x.first);
if (g != -1) {
d.emplace_back(g);
}
s.emplace_back(x.second);
}
sort(d.begin() , d.end());
sort(s.begin() , s.end());
while ((int)s.size() > (int)d.size()) {
s.pop_back();
}
auto Get = [&]() {
int val = INF;
for (int i = 0 ; i < (int)s.size() ; i += 1) {
val = min(val , s[i] + d[(int)s.size() - i - 1]);
}
return val;
};
int res = Get();
reverse(s.begin() , s.end());
reverse(d.begin() , d.end());
res = max(res , Get());
vis[node] = 2;
return dp[node] = res;
};
int res = Solve(0);
return res;
}
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n , m;
cin >> n >> m;
vector<int> a(m) , b(m) , c(m);
for (int i = 0 ; i < m ; i += 1) {
cin >> a[i] >> b[i] >> c[i];
}
cout << ferries(n , m , a , b , c) << '\n';
}
