# include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
const double pi = acos(-1);
template<class T>constexpr T inf() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T hinf() { return inf<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); }
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); }
template<class T> bool chmin(T& a,T b) { if(a > b){a = b; return true;} return false; }
template<class T> bool chmax(T& a,T b) { if(a < b){a = b; return true;} return false; }
template<class T> bool is_sqare(T a) { if(floor(sqrt(a)) * floor(sqrt(a)) == a){ return true; }return false; }
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(ll n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(ll n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
ll gcd(ll a, ll b) { if (b == 0)return a; return gcd(b, a%b); };
ll lcm(ll a, ll b) { ll g = gcd(a, b); return a / g*b; };
template<class T> using dijk = priority_queue<T, vector<T>, greater<T>>;
# define all(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(all((wpwpw)));(wpwpw).erase(unique(all((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(all((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(all((rprpr)),(rprpr).begin(),TU<char>)
# define rep(i,upupu)         for(ll i = 0, i##_len = (upupu);(i) < (i##_len);(i)++)
# define reps(i,opopo)        for(ll i = 1, i##_len = (opopo);(i) <= (i##_len);(i)++)
# define len(x)                ((int)(x).size())
# define bit(n)               (1LL << (n))
# define pb push_back
#ifdef LOCAL
#  include "_debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

struct INIT{
    INIT(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(0);
        cout << fixed << setprecision(20);
    }
}INIT;

void solve(){
    int n, m;
    cin >> n >> m;
    vector<int> a(n * m), b(n * m);
    vector<vector<int>> vis(n, vector<int>(m, 0));
    rep(i, n * m){
        cin >> a[i] >> b[i];
        a[i]--, b[i]--;
        vis[a[i]][b[i]] = i;
    }

    int ans = hinf<int>();

    rep(i, n - 4)rep(j, m){

        {
            vector<int> v;
            rep(k, 5)v.push_back(vis[i + k][j]);
            sort(all(v));
            int tmp = 0;
            int idx_v = 0;
            int idx_card = 0;
            while(idx_v < 5 && idx_card < n * m){
                if(idx_card > 0)tmp++;
                int now = 5 - idx_v;
                rep(k, now){
                    if(k + idx_card < n * m && idx_v < 5 && v[idx_v] == idx_card + k)idx_v++;
                }
                idx_card += now;
                if(idx_v == 5)break;
            }
            chmin(ans, tmp);
        }

        if(i == n - 5){
            vector<int> v;
            reps(k, 4)v.push_back(vis[i + k][j]);
            v.push_back(vis[0][j]);
            sort(all(v));
            int tmp = 0;
            int idx_v = 0;
            int idx_card = 0;
            while(idx_v < 5 && idx_card < n * m){
                if(idx_card > 0)tmp++;
                int now = 5 - idx_v;
                rep(k, now){
                    if(k + idx_card < n * m && idx_v < 5 && v[idx_v] == idx_card + k)idx_v++;
                }
                idx_card += now;
                if(idx_v == 5)break;
            }
            chmin(ans, tmp);
        }
    }
    cout << ans << endl;
}

int main(){
    int t = 1;
    //cin >> t;
    while(t--)solve();
}