#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000



int main(){
	
	int N,M;
	cin>>N>>M;
	
	dsu D(2*N);
	rep(i,M){
		int r,c;
		scanf("%d %d",&r,&c);
		r--;c--;
		
		D.merge(r,N+c);
	}
	
	auto g = D.groups();
	vector<int> x(g.size(),0),y(g.size(),0);
	
	rep(i,g.size()){
		rep(j,g[i].size()){
			if(g[i][j]<N)x[i]++;
			else y[i]++;
		}
	}
	
	int ans = Inf;
	
	{
		vector<int> dp(N+1,Inf);
		dp[0] = 0;
		rep(i,x.size()){
			vector<int> ndp(N+1,Inf);
			rep(j,N+1){
				if(dp[j]==Inf)continue;
				ndp[j] = min(ndp[j],dp[j]);
				ndp[j+x[i]] = min(ndp[j+x[i]],dp[j] + y[i]);
			}
			swap(dp,ndp);
		}
		rep(i,N+1){
			if(dp[i]==Inf)continue;
			ans = min(ans,i*dp[i] + (N-i) * (N-dp[i]) - M);
		}
	}
	
	{
		vector<int> dp(N+1,-Inf);
		dp[0] = 0;
		rep(i,x.size()){
			vector<int> ndp(N+1,-Inf);
			rep(j,N+1){
				if(dp[j]==-Inf)continue;
				ndp[j] = max(ndp[j],dp[j]);
				ndp[j+x[i]] = max(ndp[j+x[i]],dp[j] + y[i]);
			}
			swap(dp,ndp);
		}
		rep(i,N+1){
			if(dp[i]==-Inf)continue;
			ans = min(ans,i*dp[i] + (N-i) * (N-dp[i]) - M);
		}
	}
	
	cout<<ans<<endl;
	
	
    return 0;
}