#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

template<class T, bool directed>
class Dinic {
    void bfs(int s){
        fill(level.begin(),level.end(), -1);
        queue<int> Q;
        level[s] = 0;
        Q.emplace(s);
        while(!Q.empty()){
            int v = Q.front(); Q.pop();
            for (auto &&e : G[v]){
                if(e.cap > 0 && level[e.to] < 0){
                    level[e.to] = level[v] + 1;
                    Q.emplace(e.to);
                }
            }
        }
    }

    T dfs(int v, int t, T f){
        if(v == t) return f;
        for(int &i = iter[v]; i < G[v].size(); i++){
            edge &e = G[v][i];
            if(e.cap > 0 && level[v] < level[e.to]){
                T d = dfs(e.to, t, min(f,  e.cap));
                if(d == 0) continue;
                e.cap -= d;
                G[e.to][e.rev].cap += d;
                return d;
            }
        }
        return 0;
    }
public:
    struct edge {
        int to{}; T cap; int rev{};
        edge() = default;
        edge(int to, T cap, int rev) : to(to), cap(cap), rev(rev) {}
    };

    vector<vector<edge>> G;
    vector<int> level, iter;
    Dinic() = default;
    explicit Dinic(int n) : G(n), level(n), iter(n) {}

    void add_edge(int from, int to, int cap){
        G[from].emplace_back(to, cap, G[to].size());
        G[to].emplace_back(from, directed ? 0 : cap,  G[from].size()-1);
    }


    T flow(int s, int t, T lim = INF<T>){
        T ret = 0;
        while(true) {
            bfs(s);
            if(level[t] < 0 || lim == 0) break;
            fill(iter.begin(),iter.end(), 0);
            while(true){
                T f = dfs(s, t, lim);
                if(f == 0) break;
                ret += f;
                lim -= f;
            }
        }
        return ret;
    }
};
int main() {
    int h, w;
    cin >> h >> w;
    vector<vector<int>> v(h, vector<int>(w, 0));
    vector<vector<pair<int, int>>> id(h, vector<pair<int, int>>(w));
    vector<vector<int>> r(500001), c(500001);
    vector<vector<pair<int, int>>> a(500001);
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            cin >> v[i][j];
            if(v[i][j] && (r[v[i][j]].empty() || r[v[i][j]].back() != i)) r[v[i][j]].emplace_back(i);
            if(v[i][j]) {
                id[i][j].first = r[v[i][j]].size()-1;
                a[v[i][j]].emplace_back(i, j);
            }
        }
    }
    for (int j = 0; j < w; ++j) {
        for (int i = 0; i < h; ++i) {
            if(v[i][j] && (c[v[i][j]].empty() || c[v[i][j]].back() != j)) c[v[i][j]].emplace_back(j);
            if(v[i][j]) id[i][j].second = c[v[i][j]].size()-1;
        }
    }
    int ans = 0;
    for (int i = 0; i <= 500000; ++i) {
        if(a[i].empty()) continue;
        int S = r[i].size(), T = c[i].size();
        if(S == 0) continue;
        if(S == 1 || T == 1){
            ans += 1;
            continue;
        }

        Dinic<int, true> G(S+T+2);
        for (int j = 0; j < S; ++j) G.add_edge(0, j+1, 1);
        for (int j = 0; j < T; ++j) G.add_edge(S+1+j, S+T+1, 1);
        for (auto &&[j, k] : a[i]) {
            G.add_edge(id[j][k].first+1, S+1+id[j][k].second, 1);

        }
        ans += G.flow(0, S+T+1, min(S, T));

    }
    cout << ans << "\n";
    return 0;
}