#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}

#include <atcoder/maxflow>

void solve();
// CITRUS CURIO CITY / FREDERIC
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int H, W;
    cin >> H >> W;
    vector<tuple<int, int, int>> p;
    rep(i, 0, H) rep(j, 0, W){
        int a;
        cin >> a;
        p.push_back({a, i, j});
    }
    So(p);
    int ans = 0;
    auto za = [&](vector<int> &v) -> void {
        map<int, int> m;
        for (auto &x : v){
            if (!m.count(x)) m[x] = m.size();
            x = m[x];
        }
        return;
    };
    for (int l = 0, r = 0; l < H * W; l = r){
        vector<int> A, B;
        while (r != H * W && get<0>(p[l]) == get<0>(p[r])){
            A.push_back(get<1>(p[r]));
            B.push_back(get<2>(p[r]));
            r++;
        }
        if (get<0>(p[l]) == 0) continue;
        za(A), za(B);
        int X = vec_max(A) + 1, Y = vec_max(B) + 1;
        atcoder::mf_graph<int> G(X + Y + 2);
        int S = X + Y, T = S + 1;
        // cout << ans << "\n";
        // vec_out(A), vec_out(B);
        rep(i, 0, X){
            G.add_edge(S, i, 1);
            G.add_edge(i, T, 0);
        }
        rep(i, 0, Y){
            G.add_edge(S, i + X, 0);
            G.add_edge(i + X, T, 1);
        }
        rep(i, 0, A.size()){
            G.add_edge(A[i], B[i] + X, INF);
        }
        int tmp = G.flow(S, T);
        ans += tmp;
    }
    cout << ans << "\n";
}