#include<bits/stdc++.h>
#define PPque priority_queue<tuple<ll, ll, ll>, vector<tuple<ll, ll, ll>>, greater<tuple<ll, ll, ll>>>
#define Pque  priority_queue<pair<ll, ll>, vector<pair<ll, ll>>, greater<pair<ll, ll>>>
#define pque priority_queue<int, vector<int>, greater<int>>
#define umap unordered_map
#define uset unordered_set
#define rep(i, s, f) for(ll i = s; i <= f; i++)
#define per(i, s, f) for(ll i = s; i >= f; i--)
#define all0(x) (x).begin() ,(x).end()
#define all(x) (x).begin() + 1, (x).end()
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define vvvc vector<vector<vector<char>>>
#define vvvd vector<vector<vector<double>>>
#define vvvm vector<vector<vector<mint>>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvs vector<vector<string>>
#define vvc vector<vector<char>>
#define vvp vector<vector<pair<ll, ll>>>
#define vvb vector<vector<bool>>
#define vvd vector<vector<double>>
#define vvm vector<vector<mint>>
#define vp vector<pair<ll, ll>>
#define vi vector<int>
#define vl vector<ll>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vd vector<double>
#define vm vector<mint>
#define P pair<ll, ll>
#define TU tuple<ll, ll, ll>
#define rrr(l, r) mt()%(r-l+1)+l
#define ENDL '\n'

#define ull unsigned long long
typedef long long ll;
using namespace std;

////////////////////////////////////////////////////////////////////////////////////////////////////////////
//これが本当の組み込み関数ってね（笑）

template <typename T>
T or_less(vector<T> &A, T x) { //x以下で最大要素の添字 前提: sort済み 存在しない: -1
  return distance(A.begin(), upper_bound(A.begin(), A.end(), x)-1);
}
template <typename T>
T under(vector<T> &A, T x) { //x未満の最大要素の添字　前提: sort済み 存在しない: -1
  return distance(A.begin(), lower_bound(A.begin(), A.end(), x)-1);
}
template <typename T>
T or_more(vector<T> &A, T x) { //x以上で最小要素の添字　　前提: sort済み 存在しない: N .   //distanceのA.beginは添字を出すために常にA.begin() NG: A.begin() + 1
  return distance(A.begin(), lower_bound(A.begin(), A.end(), x));
}
template <typename T>
T over(vector<T> &A, T x) { //xより大きい最小要素の添字前提: sort済み 存在しない: N
  return distance(A.begin(), upper_bound(A.begin(), A.end(), x));
}
void compress(vector<ll> &A) {//小さい順に順位、大きい順にしたいならreverseはNG最後に変換
    vector<ll> temp = A;
    sort(temp.begin()+1, temp.end());
    for (int i = 1; i <= int(A.size()-1); i++) {
        A.at(i) = distance(temp.begin(), lower_bound(temp.begin()+1, temp.end(), A.at(i)));
    }
}
//////////////////////////////////////////////////////////////////////
//数学系
///////////////////////////////////////////////////////////////////////
ll round(ll x, ll i) {return ll(x + 5 * pow(10, i-1))/ll(pow(10, i)) * ll(pow(10, i));}
ll nto10(string S, ll base) {
  ll res = 0;
  reverse(all0(S));
  while(!S.empty()) {
    ll num = S.back() - '0';
    if(num < 0 || num > 9) num = 9 + S.back() - 'a' + 1;
    res = res * base + num;
    S.pop_back();
  }
  return res;
}
string toN(ll N, ll base) {
  if(N == 0) return "0";
  string ans ="";
  ll MOD = abs(base);
  while(N != 0) {
    ll first = N % MOD;
    while(first < 0) first += MOD;
    ans += to_string(first);
    N -= first;
    N /= base;
  }
  reverse(all0(ans));
  return ans;
}
vp insu_bunkai(ll N) {
  vp res;
  for (int i = 2; i * i <= N; i++) {
    ll cnt = 0;
    while(N % i == 0) {
      cnt++;
      N /= i;
    }
    if(cnt != 0) res.push_back(P(i, cnt));
  }
  if(N != 1) res.push_back(P(N, 1));
  return res;
}
struct comb_fast {//must素数
  vl fac;
  vl facinv;
  vl inv;
  ll mod_comb;
  comb_fast (ll n, ll mod) {
    mod_comb = mod;
    fac.assign(n+1, 1);
    facinv.assign(n+1, 1);
    inv.assign(n+1, 1);
    rep(i, 2, n) {
      fac.at(i) = fac.at(i-1) * i % mod_comb;
      inv.at(i) = mod_comb - inv.at(mod_comb%i) * (mod_comb/i)%mod_comb;
      facinv.at(i) = facinv.at(i-1) * inv.at(i) % mod_comb;
    }
  }
  ll get(ll n, ll k) {
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac.at(n) * (facinv.at(k) * facinv.at(n-k)%mod_comb)%mod_comb;
  }
};
vvl comb_slow(ll n, ll mod) {//計算にO(N^2)　読み取りにO(1)
  vvl v(n+1, vl(n+1, 0));
  rep(i, 0, v.size() - 1) {v.at(i).at(0) = 1;v.at(i).at(i) = 1;}
  rep(i, 1, v.size()-1) { rep(j, 1, i) { v.at(i).at(j) = v.at(i-1).at(j-1) + v.at(i-1).at(j);v.at(i).at(j) %= mod;}}
  return v;
}

double KAKUDO(double rad){return rad * 180 / 3.141592653589793;}
double RAD(double kakudo) {return kakudo / 180 * 3.141592653589793;}
ll extgcd (ll a, ll b,  ll &x, ll &y) {
  if(b == 0) { x = 1;y = 0;return a;}
  ll d = extgcd(b, a%b, y, x);
  y -= a/b * x;
  return d;
}
template <typename T>
T ceil(T a, T b) {
  assert(b != 0);
  if(a % b == 0) return a / b;
  if((a <= 0 && b < 0) || (a >= 0 && b > 0)) return a/b + 1;
  else return a / b;
}
template <typename T>
T floor(T a, T b) {
  assert(b != 0);
  if(a % b == 0) return a / b;
  if((a <= 0 && b < 0) || (a >= 0 && b > 0)) return a/b;
  else return a/b - 1;
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//グローバル変数を置くところ（情報工学意識高め）
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
ll int_max = 1001001001;
ll ll_max = 1001001001001001001LL;
const double pi = 3.141592653589793;
vl dx{0, 1, 0, -1, 0, 1, 1, -1, -1};//右から時計回り
vl dy{0, 0, -1, 0, 1, 1, -1, -1, 1};
//#pragma GCC optimize ("-O3")
//const ll mod = 1000000007;
//const ll mod = 998244353;


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void solve() {
  ll N, M;
  cin >> N >> M;
  ll T = N * M;
  vl n(T+1);
  vl m(T+1);
  map<P, ll> get; //(数字、記号) = i枚目
  rep(i, 1, T) {
    cin >> n.at(i) >> m.at(i);
    get[P(n.at(i), m.at(i))] = i;
  }



  ll ans = ll_max;

  rep(t, 1, N-3) {
    rep(k, 1, M) {
      vl needs;
      rep(tmp, 1, 5) {
        ll num = t + (tmp - 1);
        if(num > N) num -= N;
        needs.push_back(get[P(num, k)]);
      }

      sort(all0(needs));
      ll now = 0;
      ll sub = -1;
      rep(i, 0, 4) {
        ll tar = needs.at(i) - now;
        sub += (tar + (5 - i - 1))/(5 - i);
        now = now + (tar + (5 - i - 1)) / (5-i) * (5-i);
        while(i < 4 && needs.at(i+1) <= now) i++;
      }

      ans = min(sub, ans);
    }
  }

  cout << ans << endl;








}
//座標を2で割った時の”切り捨て側(左側）”を求めるには 誤:(x / 2) マイナスの時！！！ 正:floor<ll>(x, 2);
//stringでの数字の下から1桁目は 正:S.at(N-1)  誤:S.at(0)
//if(S.at(i) == 1　← charなのに1...?
// modは取りましたか...?(´・ω・｀)



int main() {
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  cout << fixed << setprecision(15);
  solve();
  return 0;
}