func_code_string: #include <bits/stdc++.h>   using namespace std;   class BLongtailHedgehog {    public:     int N, M;     vector<int> dist, deg_in, deg;     vector<vector<int>> G;     void input(std::istream& in, std::ostream& out) {       ios_base::sync_with_stdio(false);       in >> N >> M;       dist = vector<int>(N, -1);       deg_in = vector<int>(N, 0);       deg = vector<int>(N, 0);       G = vector<vector<int>>(N, vector<int>());       for (int(i) = (0); (i) < (M); ++(i)) {         int u, v;         in >> u >> v;         u--, v--;         if (u > v) swap(u, v);         G[u].push_back(v);         deg_in[v]++, deg[u]++, deg[v]++;       }     }     void bfs(int s) {       queue<int> q;       dist[s] = 1, q.push(s);       while (!q.empty()) {         int u = q.front();         q.pop();         for (auto v : G[u]) {           deg_in[v]--;           dist[v] = max(dist[v], dist[u] + 1);           if (deg_in[v] == 0) {             q.push(v);           }         }       }     }     void solve(std::istream& in, std::ostream& out) {       input(in, out);       for (int(i) = (0); (i) < (N); ++(i)) {         if (dist[i] == -1) bfs(i);       }       long long ans = 0;       for (int(i) = (0); (i) < (N); ++(i)) ans = max(ans, 1LL * dist[i] * deg[i]);       out << ans <<   n ;     }   };   int main() {     BLongtailHedgehog solver;     std::istream& in(std::cin);     std::ostream& out(std::cout);     solver.solve(in, out);     return 0;   }   