615B - Longtail Hedgehog - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
#define pb push_back
#define mp make_pair
#define pii pair <int, int>
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define F first
#define S second
const int N = 1e5 + 5;

vector<int> adj[N];
int d[N];
int dp[N];

int main(){
	fast_io;
	int n, m;
	cin >> n >> m;
	
	int a, b;
	for(int i = 0; i < m; i++)
	{
		cin >> a >> b;
		d[a]++; d[b]++;
		
		if(a < b) swap(a, b);
		
		adj[a].pb(b);
	}
	
	for(int i = 1; i <= n; i++)
	{
		if(adj[i].size() == 0) dp[i] = 1;
		else
		{
			for(int u : adj[i])
			{
				dp[i] = max(dp[i], dp[u] + 1);
			}
		}
	}
	
	ll ans = 0;
	for(int i = 1; i <= n; i++)
	{
		ans = max(ans, 1LL * dp[i] * d[i]);
	}
	
	cout << ans;
	return 0;
}