#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef int64_t lint;
#define rep(i, n) for(int i=0; i<n; i++)
#define repx(i, l, n) for(int i=l; i<n; i++)
#define all(v) v.begin(), v.end()
#define show(x) cout << #x << ": " << x << endl;
#define list(x) cout << #x << ": " << x << "  ";
#define pb push_back
using vi = vector<lint>;
using vvi = vector<vector<lint>>;
template<class T> inline void vin(vector<T>& v) { rep(i, v.size()) cin >> v.at(i); }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T> inline void drop(T x) { cout << x << endl; exit(0); }
template<class T> void vout(vector<T> v) { rep(i, v.size()) { cout << v.at(i) << ' '; } cout << endl; }
constexpr lint LINF = LLONG_MAX/2;

int main() {
	lint N, M;
	cin >> N >> M;
	vi v(N*M), w(N*M);
	rep(i, N*M) cin >> v[i] >> w[i];

	lint a=0, b=0, c=LINF, x, y, z;
	rep(i, N*M) v[i]--, w[i]--;
	rep(i, M) {
		vi t(N);
		b = -1;
		rep(j, N*M) {
			if (w[j] == i) {
				rep(k, 5) {
					t[(v[j]+k)%N]++;
					if (t[(v[j]+k)%N] == 5) {b = (v[j]+k)%N; break;}
					if ((v[j]+k) == N) break;
				}
			}
			if (b != -1) break;
		}
		// vout(t);
		// show(b)
		set<int> s;
		a = 0, x = 0;
		rep(j, N*M) {
			if (w[j] == i && v[j] >= (b-4+N)%N && v[j] <= b) s.insert(v[j]);
			x++;
			if (s.size() == 5) break;
			if (x == 5) {
				x -= 5-s.size();
				a++;
			}
		}
		chmin(c, a);
	}
	std::cout << c << '\n';
}