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

int main(){
	int n, m; cin >> n >> m;
	vector<vector<int>> ind(n, vector<int>(m));
	vector<int> x(n*m), y(n*m);
	for (int i=0; i<n*m; i++){
		cin >> x[i] >> y[i];
		x[i]--; y[i]--;
		ind[x[i]][y[i]] = i;
	}
	int ans = 998244353;
	for (int stx=0; stx<n-3; stx++){
		for (int sty=0; sty<m; sty++){
			vector<bool> seen(5);
			vector<int> pivx(5);
			for (int i=0; i<5; i++){
				pivx[i] = (stx+i)%n;
			}
			int piv = 0;
			for (int i=0; i<5; i++){
				for (int j=0; j<5; j++){
					if (x[i] == pivx[j] && y[i] == sty){
						seen[j] = true;
						piv++;
					}
				}
			}
			int zan = 0;
			for (int i=0; i<5; i++){
				if (!seen[i]){
					zan++;
				}
			}
			int tmp = 0;
			while(zan != 0){
				int gomin = 998244353;
				for (int i=0; i<5; i++){
					if (!seen[i]){
						gomin = min(gomin, ind[pivx[i]][sty]);
					}
				}
				int tobu = (gomin - piv) / zan;
				piv += tobu * zan;
				tmp += tobu;
				int hod = 0;
				for (int i=0; i<zan; i++){
					for (int j=0; j<5; j++){
						if (i+piv >= n*m) continue;
						if (x[i+piv] == pivx[j] && y[i+piv] == sty){
							seen[j] = true;
							hod++;
						}
					}
				}
				piv += hod;
				zan = 0;
				for (int i=0; i<5; i++){
					if (!seen[i]){
						zan++;
					}
				}
			}
			ans = min(ans, tmp);
		}
	}
	cout << ans << '\n';
}