#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<int> r(M), c(M);
  for (int i = 0; i < M; i++){
    cin >> r[i] >> c[i];
    r[i]--;
    c[i]--;
  }
  vector<vector<int>> E(N * 2);
  for (int i = 0; i < M; i++){
    E[r[i]].push_back(N + c[i]);
    E[N + c[i]].push_back(r[i]);
  }
  vector<int> a, b;
  int cnt = 0;
  vector<bool> used(N * 2, false);
  for (int i = 0; i < N * 2; i++){
    if (!used[i]){
      used[i] = true;
      int cnta = 0, cntb = 0;
      queue<int> Q;
      Q.push(i);
      while (!Q.empty()){
        int v = Q.front();
        Q.pop();
        if (v < N){
          cnta++;
        }
        if (v >= N){
          cntb++;
        }
        for (int w : E[v]){
          if (!used[w]){
            used[w] = true;
            Q.push(w);
          }
        }
      }
      a.push_back(cnta);
      b.push_back(cntb);
      cnt++;
    }
  }
  vector<vector<bool>> dp(N + 1, vector<bool>(N + 1, false));
  dp[0][0] = true;
  for (int i = 0; i < cnt; i++){
    for (int j = N; j >= 0; j--){
      for (int k = N; k >= 0; k--){
        if (dp[j][k]){
          dp[j + a[i]][k + b[i]] = true;
        }
      }
    }
  }
  int ans = N * N;
  for (int i = 0; i <= N; i++){
    for (int j = 0; j <= N; j++){
      if (dp[i][j]){
        ans = min(ans, i * j + (N - i) * (N - j));
      }
    }
  }
  cout << ans - M << endl;
}