#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#include <atcoder/all>
#define popcount __builtin_popcount
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;
struct unionfind{
    vector<int> par, sz;
    unionfind() {}
    unionfind(int n):par(n), sz(n, 1){
        for(int i=0; i<n; i++) par[i]=i;
    }
    int find(int x){
        if(par[x]==x) return x;
        return par[x]=find(par[x]);
    }
    void unite(int x, int y){
        x=find(x); y=find(y);
        if(x==y) return;
        if(sz[x]>sz[y]) swap(x, y);
        par[x]=y;
        sz[y]+=sz[x];
    }
    bool same(int x, int y){
        return find(x)==find(y);
    }
    int size(int x){
        return sz[find(x)];
    }
};
int dp[5050][5050], dp2[5050][5050];
bitset<5000> bs[5050], bs1[5050];

int main()
{
    int n, m;
    cin>>n>>m;
    int r[100010], c[100010];
    vector<int> vr[5050];
    for(int i=0; i<m; i++){
        cin>>r[i]>>c[i];
        r[i]--; c[i]--;
        vr[c[i]].push_back(r[i]);
        bs[r[i]][c[i]]=1;
    }
    unionfind uf(n);
    for(int i=0; i<n; i++){
        for(int j=0; j<(int)vr[i].size()-1; j++){
            uf.unite(vr[i][j], vr[i][j+1]);
        }
    }
    for(int i=0; i<n; i++){
        int x=uf.find(i);
        bs1[x]|=bs[i];
    }
    vector<P> v;
    //v.push_back({uf.size(0), bs1[uf.find(0)].count()});
    for(int i=0; i<n; i++){
        if(uf.find(i)!=i) continue;
        v.push_back({uf.size(i), bs1[i].count()});
    }
    const int INF=1e9;
    int n1=v.size();
    for(int i=0; i<=n1; i++) for(int j=0; j<=n; j++) dp[i][j]=-1, dp2[i][j]=INF;
    dp[0][0]=0, dp2[0][0]=0;
    for(int i=0; i<n1; i++){
        for(int j=0; j<=n; j++){
            if(dp[i][j]==-1) continue;
            dp[i+1][j]=max(dp[i+1][j], dp[i][j]);
            dp2[i+1][j]=min(dp2[i+1][j], dp2[i][j]);
            if(j+v[i].first<=n){
                dp[i+1][j+v[i].first]=max(dp[i+1][j+v[i].first], dp[i][j]+v[i].second);
                dp2[i+1][j+v[i].first]=min(dp2[i+1][j+v[i].first], dp2[i][j]+v[i].second);
            }
        }
    }
    int ans=n*n;
    for(int j=0; j<=n; j++){
        int x;
        if(2*j-n<=0) x=dp[n1][j];
        else x=dp2[n1][j];
        if(x==-1 || x==INF) continue;
        ans=min(ans, x*j+(n-x)*(n-j));
    }
    ans-=m;
    cout<<ans<<endl;
    return 0;
}