#include <atcoder/maxflow>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
const long long INF_LL = 2000000000000000000LL;
const int INF = 2000000000;
const long long MOD = 1000000007;
#define ll long long
#define all(x) x.begin(), x.end()
#define REP(i, a, b) for(int i = a; i < b; i++)
#define rep(i, n) REP(i, 0, n)
// typedef float double;
// typedef priority_queue prique;
typedef pair<ll, ll> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<P> vp;
typedef vector<ll> vl;
typedef vector<vi> matrix;
int dx[4] = {0, -1, 0, 1};
int dy[4] = {1, 0, -1, 0};
int sign[2] = {1, -1};
template <class T> bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}

ll modpow(ll a, ll b, ll m) {
    if(b == 0)
        return 1;
    ll t = modpow(a, b / 2, m);
    if(b & 1) {
        return (t * t % m) * a % m;
    } else {
        return t * t % m;
    }
}

struct edge {
    int to;
    ll cost;
    edge(int t, ll c) { to = t, cost = c; }
};

typedef vector<vector<edge>> graph;

// using mint = modint998244353;

int main(){
    int h, w;
    cin >> h >> w;
    vector<vector<int>> a(h, vector<int>(w));
    rep(i, h) rep(j, w) cin >> a[i][j];
    vector<vector<pair<int, int>>> t(500000);
    rep(i, h){
        rep(j, w){
            if(a[i][j] > 0) {
                t[a[i][j] - 1].push_back({i, j});
            }
        }
    }
    int ans = 0;
    for(int i = 499999; i >= 0; i--){
        if(t[i].size() > 0){
            int tmp1;
            sort(all(t[i]));
            int tmp = t[i][0].first;
            t[i][0].first = 0;
            rep(j, t[i].size() - 1){
                if(tmp < t[i][j + 1].first){
                    tmp = t[i][j + 1].first;
                    t[i][j + 1].first = t[i][j].first + 1;
                }else{
                    t[i][j + 1].first = t[i][j].first;
                }
            }
            tmp1 = t[i][t[i].size()-1].first + 1;
            int tmp2;
            sort(all(t[i]), [](auto x, auto y){return x.second < y.second;});
            tmp = t[i][0].second;
            t[i][0].second = 0;
            rep(j, t[i].size() - 1){
                if(tmp < t[i][j + 1].second){
                    tmp = t[i][j + 1].second;
                    t[i][j + 1].second = t[i][j].second + 1;
                }else{
                    t[i][j + 1].second = t[i][j].second;
                }
            }
            tmp2 = t[i][t[i].size()-1].second + 1;
            mf_graph<int> g(tmp1 + tmp2 + 2);
            rep(j, tmp1) g.add_edge(tmp1 + tmp2, j, 1);
            rep(j, tmp2) g.add_edge(j + tmp1, tmp1 + tmp2 + 1, 1);
            rep(j, t[i].size()){
                g.add_edge(t[i][j].first, t[i][j].second + tmp1, 1);
            }
            ans += g.flow(tmp1 + tmp2, tmp1 + tmp2 + 1);
        }
    }
    cout << ans << endl;
}