#include <bits/stdc++.h> 
using namespace std;
using ll =long long;
#define all(v) v.begin(),v.end()
 #define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)

ll INF=2e18;


int main() {
    ios::sync_with_stdio(false);
  cin.tie(0);
  
  ll N,M;cin>>N>>M;
  vector<vector<ll>> od(M,vector<ll> (N+1));
  for(ll i=1;i<=N*M;i++) {
    ll n,m;cin>>n>>m;
    m--;
    od[m][n]=i;
  }

  ll ans=INF;
  for(ll i=0;i<M;i++) {
    for(ll j=1;j<=N-3;j++) {
      vector<ll> note(0);
      for(ll h=0;h<5;h++) {
        if(j+h<=N) note.push_back(od[i][j+h]);
        else note.push_back(od[i][1]);
      }
    sort(all(note));
    ll count=0;

    ll ind=0;
    
    ll last=0;

    while(ind<5) {
    count+=(note[ind]-last-1)/(5-ind);
    last+=(note[ind]-last-1)/(5-ind)*(5-ind);

    last+=(5-ind);
    count++;

    while(ind<5&&last>=note[ind]) {
      ind++;
    }
    }

    count--;
    ans=min(ans,count);
    }
  }

  cout<<ans<<endl;
}