#include "testlib.h"

#include <algorithm>
#include <iostream>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)

int N,M;
int pos[501][500]={};
int sfPos[5]={};

int solve_per_sfPos(){
  int ans=0;
  int remain=0, p=0;
  rep(i,5){
    remain+=sfPos[i]-p; p=sfPos[i]+1;
    ans+=remain/(5-i);
    remain%=(5-i);
  }
  return ans;
}

int main(){
  registerValidation();
  N = inf.readInt(5,500);
  inf.readSpace();
  M = inf.readInt(1,500);
  inf.readEoln();
  rep(i,N*M){
    int n = inf.readInt(1,N);
    inf.readSpace();
    int m = inf.readInt(1,M);
    inf.readEoln();
    n--; m--;
    pos[n][m]=i;
  }
  rep(i,M) pos[N][i]=pos[0][i];
  inf.readEof();

  int ans=1000000000;
  for(int ns=0; ns<=N-4; ns++) rep(m,M) {
    rep(i,5) sfPos[i]=pos[ns+i][m];
    sort(sfPos,sfPos+5);
    ans=min(ans,solve_per_sfPos());
  }
  cout<<ans<<"\n";

  return 0;
}