#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  constexpr int C = 5;
  int n, m; cin >> n >> m;
  vector<int> a(n * m), b(n * m); REP(i, n * m) cin >> a[i] >> b[i], --a[i], --b[i];
  vector cards(m, vector(n, -1));
  REP(i, n * m) cards[b[i]][a[i]] = i;
  int ans = n * m;
  const auto solve = [&](vector<int> sf) -> void {
    ranges::sort(sf, greater<int>());
    while (!sf.empty() && sf.back() < C) sf.pop_back();
    int op = 0;
    for (int i = C; !sf.empty();) {
      const int num = (sf.back() - i + 1 + ssize(sf) - 1) / ssize(sf);
      op += num;
      i += ssize(sf) * num;
      while (!sf.empty() && sf.back() < i) sf.pop_back();
    }
    chmin(ans, op);
  };
  REP(i, m) {
    for (int j = 0; j + C <= n; ++j) {
      vector<int> sf(C);
      REP(k, C) sf[k] = cards[i][(j + k) % n];
      solve(sf);
    }
  }
  cout << ans << '\n';
  return 0;
}