using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Threading;
using System.Text;
using System.Text.RegularExpressions;
using System.Diagnostics;
using static util;
using P = pair<int, int>;

class Program {
    static void Main(string[] args) {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        var solver = new Solver(sw);
        // var t = new Thread(solver.solve, 1 << 28); // 256 MB
        // t.Start();
        // t.Join();
        solver.solve();
        sw.Flush();
    }
}

class Solver {
    StreamWriter sw;
    Scan sc;
    void Prt(string a) => sw.WriteLine(a);
    void Prt<T>(IEnumerable<T> a) => Prt(string.Join(" ", a));
    void Prt(params object[] a) => Prt(string.Join(" ", a));
    public Solver(StreamWriter sw) {
        this.sw = sw;
        this.sc = new Scan();
    }

    public void solve() {
        int h, w;
        sc.Multi(out h, out w);
        var dich = new Dictionary<long, int>();
        var dicw = new Dictionary<long, int>();
        int N = 0;
        var edges = new List<P>();
        for (int i = 0; i < h; i++)
        {
            var a = sc.IntArr;
            for (int j = 0; j < w; j++)
            {
                if (a[j] == 0) continue;
                long pi = i * (long)M + a[j];
                long pj = j * (long)M + a[j];
                if (!dich.ContainsKey(pi)) {
                    dich.Add(pi, N);
                    ++N;
                }
                if (!dicw.ContainsKey(pj)) {
                    dicw.Add(pj, N);
                    ++N;
                }
                int ci = dich[pi];
                int cj = dicw[pj];
                edges.Add(new P(ci, cj));
            }
        }
        var mf = new MaxFlow(N + 2);
        int S = N, T = N + 1;
        foreach (var item in dich.Values)
        {
            mf.add_edge(S, item, 1);
        }
        foreach (var item in dicw.Values)
        {
            mf.add_edge(item, T, 1);
        }
        foreach (var item in edges)
        {
            mf.add_edge(item.v1, item.v2, 1);
        }
        Prt(mf.run(S, T));
    }
}

class pair<T, U> : IComparable<pair<T, U>> {
    public T v1;
    public U v2;
    public pair() : this(default(T), default(U)) {}
    public pair(T v1, U v2) { this.v1 = v1; this.v2 = v2; }
    public int CompareTo(pair<T, U> a) {
        int c = Comparer<T>.Default.Compare(v1, a.v1);
        return c != 0 ? c : Comparer<U>.Default.Compare(v2, a.v2);
    }
    public override string ToString() => $"{v1} {v2}";
    public void Deconstruct(out T a, out U b) { a = v1; b = v2; }
}
static class util {
    public static readonly int M = 1000000007;
    // public static readonly int M = 998244353;
    public static readonly long LM = 1L << 60;
    public static readonly double eps = 1e-11;
    public static void DBG(string a) => Console.Error.WriteLine(a);
    public static void DBG<T>(IEnumerable<T> a) => DBG(string.Join(" ", a));
    public static void DBG(params object[] a) => DBG(string.Join(" ", a));
    public static void Assert(params bool[] conds) {
        if (conds.Any(x => !x)) throw new Exception();
    }
    public static pair<T, U> make_pair<T, U>(T v1, U v2) => new pair<T, U>(v1, v2);
    public static int CompareList<T>(IList<T> a, IList<T> b) where T : IComparable<T> {
        for (int i = 0; i < a.Count && i < b.Count; i++)
            if (a[i].CompareTo(b[i]) != 0) return a[i].CompareTo(b[i]);
        return a.Count.CompareTo(b.Count);
    }
    public static bool inside(int i, int j, int h, int w) => i >= 0 && i < h && j >= 0 && j < w;
    public static readonly int[] dd = { 0, 1, 0, -1 };
    // static readonly string dstring = "RDLU";
    public static IEnumerable<P> adjacents(int i, int j) {
        for (int k = 0; k < 4; k++) yield return new P(i + dd[k], j + dd[k ^ 1]);
    }
    public static IEnumerable<P> adjacents(int i, int j, int h, int w) {
        for (int k = 0; k < 4; k++) if (inside(i + dd[k], j + dd[k ^ 1], h, w))
            yield return new P(i + dd[k], j + dd[k ^ 1]);
    }
    public static IEnumerable<P> adjacents(this P p) => adjacents(p.v1, p.v2);
    public static IEnumerable<P> adjacents(this P p, int h, int w) => adjacents(p.v1, p.v2, h, w);
    public static IEnumerable<int> all_subset(this int p) {
        for (int i = 0; ; i = i - p & p) {
            yield return i;
            if (i == p) break;
        }
    }
    public static Dictionary<T, int> compress<T>(this IEnumerable<T> a)
        => a.Distinct().OrderBy(v => v).Select((v, i) => new { v, i }).ToDictionary(p => p.v, p => p.i);
    public static Dictionary<T, int> compress<T>(params IEnumerable<T>[] a)
        => compress(a.SelectMany(x => x));
    public static T[] inv<T>(this Dictionary<T, int> dic) {
        var res = new T[dic.Count];
        foreach (var item in dic) res[item.Value] = item.Key;
        return res;
    }
    public static void swap<T>(ref T a, ref T b) where T : struct { var t = a; a = b; b = t; }
    public static void swap<T>(this IList<T> a, int i, int j) where T : struct {
        var t = a[i]; a[i] = a[j]; a[j] = t;
    }
    public static T[] copy<T>(this IList<T> a) {
        var ret = new T[a.Count];
        for (int i = 0; i < a.Count; i++) ret[i] = a[i];
        return ret;
    }
}

class Scan {
    StreamReader sr;
    public Scan() { sr = new StreamReader(Console.OpenStandardInput()); }
    public Scan(string path) { sr = new StreamReader(path); }
    public int Int => int.Parse(Str);
    public long Long => long.Parse(Str);
    public double Double => double.Parse(Str);
    public string Str => ReadLine.Trim();
    public string ReadLine => sr.ReadLine();
    public pair<T, U> Pair<T, U>() {
        T a; U b;
        Multi(out a, out b);
        return new pair<T, U>(a, b);
    }
    public P P => Pair<int, int>();
    public int[] IntArr => StrArr.Select(int.Parse).ToArray();
    public long[] LongArr => StrArr.Select(long.Parse).ToArray();
    public double[] DoubleArr => StrArr.Select(double.Parse).ToArray();
    public string[] StrArr => Str.Split(new[]{' '}, StringSplitOptions.RemoveEmptyEntries);
    bool eq<T, U>() => typeof(T).Equals(typeof(U));
    T ct<T, U>(U a) => (T)Convert.ChangeType(a, typeof(T));
    T cv<T>(string s) => eq<T, int>()    ? ct<T, int>(int.Parse(s))
                       : eq<T, long>()   ? ct<T, long>(long.Parse(s))
                       : eq<T, double>() ? ct<T, double>(double.Parse(s))
                       : eq<T, char>()   ? ct<T, char>(s[0])
                                         : ct<T, string>(s);
    public void Multi<T>(out T a) => a = cv<T>(Str);
    public void Multi<T, U>(out T a, out U b) {
        var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]);
    }
    public void Multi<T, U, V>(out T a, out U b, out V c) {
        var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]);
    }
    public void Multi<T, U, V, W>(out T a, out U b, out V c, out W d) {
        var ar = StrArr; a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]);
    }
    public void Multi<T, U, V, W, X>(out T a, out U b, out V c, out W d, out X e) {
        var ar = StrArr;
        a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]);
    }
    public void Multi<T, U, V, W, X, Y>(out T a, out U b, out V c, out W d, out X e, out Y f) {
        var ar = StrArr;
        a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]);
        d = cv<W>(ar[3]); e = cv<X>(ar[4]); f = cv<Y>(ar[5]);
    }
}

class MaxFlow {
    public class edge {
        public int to;
        public long cap;
        public int rev;
        public edge(int t, long c, int r) { to = t; cap = c; rev = r; }
    }
    int V;
    List<edge>[] G;
    int[] itr, lev;
    public List<edge>[] getEdges() => G;

    public MaxFlow(int v) {
        V = v; G = new List<edge>[v];
        for (int i = 0; i < v; ++i) G[i] = new List<edge>();
    }
    public void add_edge(int frm, int to, long c) => add_edge(frm, to, c, true);
    public void add_edge(int frm, int to, long c, bool dir) {
        G[frm].Add(new edge(to, c, G[to].Count));
        G[to].Add(new edge(frm, dir ? 0 : c, G[frm].Count - 1));
    }
    void bfs(int s) {
        lev = new int[V];
        for (int i = 0; i < V; ++i) lev[i] = -1;
        var q = new Queue<int>();
        lev[s] = 0;
        q.Enqueue(s);
        while (q.Count > 0) {
            int v = q.Dequeue();
            foreach (var e in G[v]) {
                if (e.cap > 0 && lev[e.to] < 0) {
                    lev[e.to] = lev[v] + 1;
                    q.Enqueue(e.to);
                }
            }
        }
    }
    long dfs(int v, int t, long f) {
        if (v == t) return f;
        for (; itr[v] < G[v].Count; ++itr[v]) {
            var e = G[v][itr[v]];
            if (e.cap > 0 && lev[v] < lev[e.to]) {
                long d = dfs(e.to, t, f < e.cap ? f : e.cap);
                if (d > 0) {
                    e.cap -= d;
                    G[e.to][e.rev].cap += d;
                    return d;
                }
            }
        }
        return 0;
    }

    public long run(int s, int t) {
        long ret = 0;
        bfs(s);
        while (lev[t] >= 0) {
            itr = new int[V];
            long f;
            while ((f = dfs(s, t, util.LM)) > 0) ret += f;
            bfs(s);
        }
        return ret;
    }
}