#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
	int n, m;
	cin >> n >> m;
	vector<vector<int>> flg(m, vector<int>(n));
	rep(i,n*m){
		int a, b;
		cin >> a >> b;
		--a;--b;
		flg[b][a] = i+1;
	}
	int ans = n*m;
	rep(i,m){
		for(int j=1;j<=n-3;j++){
			vector<int> vs;
			for(int k=0;k<5;k++){
				vs.push_back(flg[i][(j+k)%n]);
			}
			sort(vs.begin(),vs.end());
			dbg(vs);
			int tmp = 0;
			int cnt = 0;
			int now = 5;
			while(true){
				while(cnt<5 && vs[cnt]<=now) cnt++;
				if(cnt==5) break;
				int nxt = vs[cnt];
				int val = (nxt-now+5-cnt-1)/(5-cnt);
				now += val*(5-cnt);
				tmp += val;
			}
			ans = min(ans, tmp);
		}
	}
	cout << ans << endl;
	return 0;
}