#include "bits/stdc++.h"
#include <unordered_map>
#include <unordered_set>

#include <stdio.h>
#include <math.h>
#include <cassert>

#include "atcoder/all"
#include <float.h>

//#include <boost/multiprecision/cpp_int.hpp>
//using namespace boost::multiprecision;
// std::fixed << std::setprecision(10) <<

using namespace std;
using namespace atcoder;

using ll = long long;
using ull = unsigned long long;
using mint = modint998244353;
using mint2 = modint1000000007;

const double eps = 1e-9;

#define REP(i, n) for (ll i = 0; i < ll(n); ++i)
#define REPI(i, init, n) for (ll i = init; i < ll(n); ++i)
#define REPD(i, init) for (ll i = init; i >=0; --i)
#define REPDI(i, init, n) for (ll i = init; i >=n; --i)
#define REPE(i, c) for (const auto& i : c)
#define TCASE ll t; cin >> t; REP(i, t)

using vl = vector<ll>;
#define VL(a, n) vector<ll> a; a.assign(n, 0);
#define VLI(a, n) vector<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define VSI(a, n) vector<string> a; a.assign(n, ""); for(auto& x : a) cin >> x;
using vvl = vector<vector<ll>>;
#define VVLI(a, n, m, init) vector<vector<ll>> a(n); for(auto& x : a) x.assign(m, init);
using pl = pair<ll, ll>;

struct uv { ll u; ll v; ll c; };
#define VUVI(a, n) vector<uv> a; a.assign(n, {0, 0, 1}); for(auto& x : a) {cin >> x.u >> x.v; x.u--; x.v--;}
#define VUVCI(a, n) vector<uv> a; a.assign(n, {0, 0, 0}); for(auto& x : a) {cin >> x.u >> x.v >> x.c; x.u--; x.v--;}
vvl to_edge(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) ret[x.u].push_back(x.v); return ret; }
vvl to_edge_d(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) { ret[x.u].push_back(x.v); ret[x.v].push_back(x.u); } return ret; }

template <class T = long long> using pql = priority_queue<T>;
template <class T = long long> using pqg = priority_queue<T, vector<T>, greater<T>>;
using vm = vector<mint>;
using vvm = vector<vm>;

const char* YES = "Yes";
const char* NO = "No";
void yn(bool f) { std::cout << (f ? YES : NO) << endl; };
template<class T> void ov(const T& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << *it; } };
template<> void ov(const vm& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << it->val(); } };

const ll llhuge = 1LL << 60; //十分でかいが多少足しても溢れない数値
template<class T, class U> bool chmin(T& a, const U& b) { ll olda = a; a = min(a, b); return olda != a; }
template<class T, class U> bool chmax(T& a, const U& b) { ll olda = a; a = max(a, b); return olda != a; }
template<class T> void mysort(T& v) { std::sort(begin(v), end(v)); };
template<class T, class U> void mysort(T& v, U pr) { std::sort(begin(v), end(v), pr); };
template<class T> void myrev(T& v) { std::reverse(begin(v), end(v)); };

//この組み合わせを引くのにかかる最大数
ll cnt(const vector<ll>& t) {
	if (t.size() != 5) return llhuge;

	ll cc = 0; //現在の手持ちのうち、残す枚数。
	ll ret = 0;
	ll it = 0;//現在引いた枚数
	//4までは初期手札
	REPE(e, t) if (e <= 4) cc++;
	it = 4;

	while (cc != 5) {
		ll nt = t[cc]; //次に引くカードの位置
		ll dr = 5 - cc; //一度に引ける枚数

		ll cnt = (nt - it + dr - 1) / dr; //引く回数
		ret += cnt;
		it += cnt * dr;
		
		cc = 0;
		REPE(e, t) if (e <= it) cc++;
	}
	return ret;
}

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	ll n, m;
	cin >> n >> m;

	vector<vector<vector<ll>>> al(m, vector<vector<ll>>(n, vector<ll>()));

	REP(i, n * m) {
		ll ni, mi;
		cin >> ni >> mi;
		ni--; mi--;

		for (int nt = ni; nt >= max(0LL, ni - 4); nt--) {
			al[mi][nt].push_back(i);
		}
		if (ni == 0) {
			al[mi][n - 4].push_back(i);
		}
	}

	ll ans = llhuge;
	REP(i, m) REP(j, n) {
		chmin(ans, cnt(al[i][j]));
	}

	cout << ans << endl;
}