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

#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
using ll=long long int;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

struct UnionFind{
   vector<int> par; int n;
   UnionFind(){}
   UnionFind(int _n):par(_n,-1),n(_n){}
   int root(int x){return par[x]<0?x:par[x]=root(par[x]);}
   bool same(int x,int y){return root(x)==root(y);}
   int size(int x){return -par[root(x)];}
   bool unite(int x,int y){
      x=root(x),y=root(y); if(x==y)return false;
      if(size(x)>size(y))swap(x,y);
      par[y]+=par[x]; par[x]=y; n--; return true;
   }
};

using P=pair<int,int>;
P cnt[10002];
bitset<5002> dp[5002];
int rui[5002][5002];

int main(){
   int n,m;
   cin>>n>>m;
   UnionFind uni(n*2);
   rep(i,0,m){
      int x,y;
      cin>>x>>y;
      x--; y--;
      uni.unite(x,y+n);
   }
   
   int X=0,Y=0;
   rep(i,0,n){
      if(uni.size(i)==1)X++;
      else cnt[uni.root(i)].first++;
   }
   rep(i,n,n*2){
      if(uni.size(i)==1)Y++;
      else cnt[uni.root(i)].second++;
   }

   dp[0][0]=1;
   rep(x,0,n*2)if(cnt[x].first!=0 or cnt[x].second!=0){
      auto [a,b]=cnt[x];
      for(int i=n-a;i>=0;i--)dp[i+a]|=dp[i]<<b;
   }
   rep(a,0,n+1)rep(b,0,n+1)if(dp[a][b]){
      rui[a][b]++;
      rui[a+X+1][b]--;
      rui[a][b+Y+1]--;
      rui[a+X+1][b+Y+1]++;
   }
   rep(i,0,n+1)rep(j,0,n+1)rui[i+1][j]+=rui[i][j];
   rep(i,0,n+1)rep(j,0,n+1)rui[i][j+1]+=rui[i][j];
   int res=inf;
   rep(a,0,n+1)rep(b,0,n+1)if(rui[a][b]){
      chmin(res,a*b+(n-a)*(n-b)-m);
   }
   cout<<res<<'\n';
   return 0;
}