aropan_pairs_java_solution

import java.io.*;
import java.util.*;
import static java.lang.Math.abs;

public class pairs_in_matrix_ar
{
    static int MAXN = 81;
    static int MAXT = MAXN * MAXN;
    static int MAXK = MAXT * 8;
    static int INF = (int)1e+9 + 1;

    static int a[][] = new int[MAXN][MAXN];

    static int next[] = new int[MAXK];
    static int dst[] = new int[MAXK];
    static int src[] = new int[MAXK];
    static int flow[] = new int[MAXK];
    static int dist[] = new int[MAXK];
    static int last[] = new int[MAXT];
    static int phi[] = new int[MAXT];
    static int d[] = new int[MAXT];
    static int p[] = new int[MAXT];

    static int frs[] = new int[MAXK];
    static int lst[] = new int[MAXK];
    static int nxt[] = new int[MAXK];
    static int val[] = new int[MAXK];

    static int n, m, k, t, c = 0;
    static int ans;
    static int cnt;

    public static void adde(int x, int y, int f, int c)
    {
        k += 1;
        src[k] = x;
        dst[k] = y;
        flow[k] = f;
        dist[k] = c;
        next[k] = last[x];
        last[x] = k;
    }

    public static void adde(int x, int y, int c)
    {
        adde(x, y, 1, c);
        adde(y, x, 0, -c);
    }

    public static void eadd(int i, int v)
    {
        c += 1;
        if (frs[i] == 0) frs[i] = c;
        if (lst[i] != 0) nxt[lst[i]] = c;
        val[c] = v;
        lst[i] = c;
    }

    public static int dijkstra(int st)
    {
        for (int i = 1; i <= t; i++)
        {
            d[i] = INF;
            p[i] = -1;
        }
        for (int i = 0; i <= c; i++)
        {
            frs[i] = 0;
            lst[i] = 0;
            nxt[i] = 0;
        }
        c = 0;

        p[st] = d[st] = 0;
        eadd(0, st);
        for (int l = 0; l < t; l++)
            for (int j = frs[l]; j > 0; j = nxt[j])
            {
                int x = val[j];
                if (d[x] != l)
                    continue;
                for (int i = last[x]; i > 0; i = next[i])
                {
                    cnt += 1;
                    if (flow[i] == 0)
                        continue;
                    int y = dst[i];
                    int v = l + dist[i] + phi[x] - phi[y];
                    if (v < d[y])
                    {
                        d[y] = v;
                        p[y] = i;
                        eadd(v, y);
                    }
                }
            }
        int res = d[t] + phi[t] - phi[st];
        for(int i = 1; i <= t; ++i)
            phi[i] += p[i] != -1? d[i] : d[t];
        return res;
    }

    public static void main(String[] args) throws FileNotFoundException
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        int n = in.readInt();
        int m = in.readInt();
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= m; j++)
                a[i][j] = in.readInt();
        k = 1;
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= m; j++)
                if (((i + j) & 1) != 0)
                    for (int dx = -1; dx <= 1; dx += 1)
                    {
                        for (int dy = dx == 0? -1 : 0; dy <= 1; dy += 2)
                        {
                            int x = (i - 1) * m + j;
                            int y = (i + dx - 1) * m + j + dy;
                            i += dx;
                            j += dy;
                            if (1 <= i && i <= n && 1 <= j && j <= m)
                            {
                                int c = a[i - dx][j - dy] != a[i][j]? 1 : 0;
                                adde(x, y, c);
                            }
                            i -= dx;
                            j -= dy;
                        }
                    }
        t = n * m + 2;
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= m; j++)
                if (((i + j) & 1) != 0)
                    adde(t - 1, (i - 1) * m + j, 0);
                else
                    adde((i - 1) * m + j, t, 0);


        for (int i = 1; i <= n * m / 2; i++)
        {
            int v = dijkstra(t - 1);
    //      cout << v << endl;
            ans += v;
            int x = t;

            while (x != t - 1)
            {
                flow[p[x] ^ 0] -= 1;
                flow[p[x] ^ 1] += 1;
                x = src[p[x]];
            }
        }
        out.printLine(ans);
        out.close();
    }
}

class InputReader {

    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public InputReader(InputStream stream) {
        this.stream = stream;
    }

    public int read() {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars) {
            curChar = 0;
            try {
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }

    public int readInt() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        int res = 0;
        do {
            if (c < '0' || c > '9')
                throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        } while (!isSpaceChar(c));
        return res * sgn;
    }

    public long readLong() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        long res = 0;
        do {
            if (c < '0' || c > '9')
                throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        } while (!isSpaceChar(c));
        return res * sgn;
    }

    public boolean isSpaceChar(int c) {
        if (filter != null)
            return filter.isSpaceChar(c);
        return isWhitespace(c);
    }

    public static boolean isWhitespace(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    public interface SpaceCharFilter {
        public boolean isSpaceChar(int ch);
    }
}

class OutputWriter {
    private final PrintWriter writer;

    public OutputWriter(OutputStream outputStream) {
        writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public OutputWriter(Writer writer) {
        this.writer = new PrintWriter(writer);
    }

    public void print(Object...objects) {
        for (int i = 0; i < objects.length; i++) {
            if (i != 0)
                writer.print(' ');
            writer.print(objects[i]);
        }
    }

    public void printLine(Object...objects) {
        print(objects);
        writer.println();
    }

    public void close() {
        writer.close();
    }

    }