题目

#include <bits/stdc++.h>
using namespace std;
#define int long long#define pb push_back#define fi first#define se second#define lson p << 1#define rson p << 1 | 1#define ll long longconst int maxn = 1e6 + 5, inf = 1e9, maxm = 4e4 + 5, base = 37;
const int N = 4e3;
const int mod = 1e9 + 7;
// const int mod = 998244353;
// const __int128 mod = 212370440130137957LL;int n, m;
int a[maxn];//long long ? maxn ? n? m?
void solve(){ll res = 0;cin >> n >> m;vector<vector<int>> G(n + 1);vector<vector<pair<int, int>>> req(n + 1);vector<int> ind(n + 1), f(n + 1, 1);for(int i = 1; i <= m; i++){int x, y, z;cin >> x >> y >> z;G[y].pb(x);G[z].pb(x);ind[x] += 2;req[x].pb({y, z});}int cnt = 0;queue<int> q;for(int i = 1; i <= n; i++){if(ind[i] == 0){q.push(i);cnt++;f[i] = 1;}}while(!q.empty()){int u = q.front();q.pop();for(auto [x, y] : req[u]){f[u] = max(f[u], f[x] + f[y]);}res += f[u];if(res > inf){cout << -1 << '\n';return;}for(auto v : G[u]){ind[v]--;if(ind[v] == 0){q.push(v);cnt++;}}}if(cnt != n){cout << -1 << '\n';return;}cout << res << '\n';
}signed main(){ios::sync_with_stdio(0);cin.tie(0);cout << fixed << setprecision(9);int T = 1;// cin >> T;while (T--){solve();}return 0;
}