#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001



int main(){
	
	int N,M;
	cin>>N>>M;
	
	vector pos(N,vector<int> (M));
	rep(i,N*M){
		int x,y;
		cin>>x>>y;
		x--,y--;
		pos[x][y] = i;
	}
	int ans= Inf32;
	rep(ii,M){
		rep(j,N-3){
			vector<int> ps;
			rep(k,5){
				int t = (j+k)%N;
				ps.push_back(pos[t][ii]);
			}
			sort(ps.begin(),ps.end());
			int correct = 0;
			rep(i,ps.size()){
				if(ps[i]<5)correct ++;
			}
			int nxt = 5;
			int num = 0;
			while(correct!=5){
				int dist = ps[correct]+1 - nxt;
				int Cnt = (dist+(5-correct)-1) / (5-correct);
				num += Cnt;
				nxt += (5-correct) * Cnt;
				correct = 0;
				rep(i,ps.size()){
					if(ps[i]<nxt)correct++;
				}
			}
			ans = min(ans,num);
		}
	}
	cout<<ans<<endl;
	
	return 0;
}