#include <bits/stdc++.h>
using namespace std;
const int INF = 10000;
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<int> dp1(N * 2 - 1, -INF);
  vector<int> dp2(N * 2 - 1, INF);
  dp1[0] = 0;
  dp2[0] = 0;
  for (int i = 0; i < cnt; i++){
    for (int j = N * 2 - 2; j >= 0; j--){
      if (j + a[i] + b[i] < N * 2 - 1){
        if (dp1[j] != -INF){
          dp1[j + a[i] + b[i]] = max(dp1[j + a[i] + b[i]], dp1[j] + a[i] - b[i]);
        }
        if (dp2[j] != INF){
          dp2[j + a[i] + b[i]] = min(dp2[j + a[i] + b[i]], dp2[j] + a[i] - b[i]);
        }
      }
    }
  }
  int ans = N * N;
  for (int i = 0; i < N * 2 - 1; i++){
    if (dp1[i] != -INF){
      int sa = (i + dp1[i]) / 2;
      int sb = (i - dp1[i]) / 2;
      ans = min(ans, sa * sb + (N - sa) * (N - sb));
    }
    if (dp2[i] != INF){
      int sa = (i + dp2[i]) / 2;
      int sb = (i - dp2[i]) / 2;
      ans = min(ans, sa * sb + (N - sa) * (N - sb));
    }
  }
  cout << ans - M << endl;
}