#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

#define pb push_back

const ld pi = 3.14159265358979323846;
const ll INF = 1e18;
const int mod = (int)1e9 + 7;

template<typename T>
T chmax(T a, T b) {
    return a > b ? a : b;
}

template<typename T>
T chmin(T a, T b) {
    return a > b ? b : a;
}

const int N = 3e3 + 1, M = N * 2;


void solve() {
     int n, m;
    cin >> n >> m;
    const ll INF = 1e18;
    vector<vector<pair<int, ll>>> adj(n + 1);

    for (int i = 0; i < m; ++i) {
        int u, v;
        ll w;
        cin >> u >> v >> w;
        adj[u].emplace_back(v, w);
    }

    vector<ll> f(n + 1, INF);
    vector<int> vs(n + 1, 0);
  
    f[1] = 0;
    priority_queue<pair<ll, ll>, vector<pair<ll, ll>>, greater<>> q;

    q.push({0, 1});

    while (!q.empty()) {
        auto p = q.top();
        q.pop();

        int u = p.second;
        if(vs[u] > n){
            continue;
        }
        vs[u]++;

        for(auto g : adj[u]){
            int v = g.first, w = g.second;
            if(f[v] > chmax(0ll, f[u] + w)){
                if(vs[v] == 2){
                    f[v] = (w < 0 ? 0 : chmax(0ll, f[u] + w));
                }
                else{
                    f[v] = chmax(0ll, f[u] + w);
                }
                q.push({f[v], v});
            }
        }
    }

    cout << f[n] << endl;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int t = 1;
    // cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}