#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int main(){
	
	int H,W;
	cin>>H>>W;
	
	vector<vector<int>> A(H,vector<int>(W));
	
	vector<vector<pair<int,int>>> N(500001);
	
	rep(i,H){
		rep(j,W){
			cin>>A[i][j];
			
			N[A[i][j]].emplace_back(i,j);
			
		}
	}
	
	int ans = 0;
	vector<int> h(H,-1);
	vector<int> w(W,-1);
	rep(i,N.size()){
		if(i==0)continue;
		vector<int> y,x;
		rep(j,N[i].size()){
			int yy = N[i][j].first,xx = N[i][j].second;
			if(h[yy]==-1){
				h[yy] = y.size();
				y.push_back(yy);
			}
			if(w[xx]==-1){
				w[xx] = x.size();
				x.push_back(xx);
			}
		}
		sort(y.begin(),y.end());
		sort(x.begin(),x.end());
		
		mf_graph<int> G(y.size()+x.size()+2);
		int S = y.size()+x.size();
		int T = S+1;
		
		rep(j,N[i].size()){
			int yy = N[i][j].first,xx = N[i][j].second;
			G.add_edge(h[yy],y.size() + w[xx],1);
		}
		
		rep(j,y.size()){
			G.add_edge(S,j,1);
		}
		rep(j,x.size()){
			G.add_edge(y.size()+j,T,1);
		}
		
		ans += G.flow(S,T);
		rep(j,N[i].size()){
			int yy = N[i][j].first,xx = N[i][j].second;
			h[yy] = -1;
			w[xx] = -1;
		}
		
	}
	
	
	
	
	cout<<ans<<endl;
	
    return 0;
}