#include <bits/stdc++.h>
using namespace std;

#include <atcoder/maxflow>

#ifdef _RUTHEN
#include <debug.hpp>
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int H, W;
    cin >> H >> W;
    V<V<int>> A(H, V<int>(W));
    rep(i, H) rep(j, W) cin >> A[i][j];
    map<int, int> mph[H], mpw[W];
    atcoder::mf_graph<int> G(H * W * 2 + 2);
    int s = H * W * 2, t = s + 1;
    rep(i, H) {
        rep(j, W) {
            if (A[i][j] == 0) continue;
            if (mph[i].count(A[i][j]) == 0) {
                mph[i][A[i][j]] = i * W + j;
                G.add_edge(s, i * W + j, 1);
            }
            if (mpw[j].count(A[i][j]) == 0) {
                mpw[j][A[i][j]] = i * W + j;
                G.add_edge(i * W + j + H * W, t, 1);
            }
            G.add_edge(mph[i][A[i][j]], mpw[j][A[i][j]] + H * W, 1);
        }
    }
    int ans = G.flow(s, t);
    cout << ans << '\n';
    return 0;
}