func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<int> adj[1000000 + 342];   set<int> ans;   bool incl[1000000 + 342];   bool isleader[1000000 + 342];   map<pair<int, int>, bool> egd;   int main() {     ios::sync_with_stdio(false);     int n, m, x, y;     cin >> n >> m;     for (int i = 0; i < m; i++) {       cin >> x >> y;       if (egd[make_pair(x, y)] == false) {         adj[x].push_back(y);         egd[make_pair(x, y)] = true;       }     }     for (int i = 1; i <= n; i++) {       if (incl[i] == false) {         for (auto next : adj[i]) {           if (next > i)             if (incl[next] == false) {               incl[next] = true;             }         }       }     }     for (int i = n; i >= 1; i--) {       if (incl[i] == false) {         ans.insert(i);         for (auto next : adj[i]) {           incl[next] = true;         }       }     }     cout << ans.size() <<   n ;     for (auto bc : ans) cout << bc <<    ;     return 0;   }   