import java.util.*;
import java.math.*;
import static java.lang.Math.*;

public class PalindromeMatrix {

    boolean hasBit(int mask, int pos) {
        return (mask & (1 << pos)) != 0;
    }

    public int minChange(String[] A, int rowCount, int columnCount) {
        int n = A.length, m = A[0].length();
        int[] goodMasksN = new int[5000];
        int cntN = 0;
        int[] goodMasksM = new int[5000];
        int cntM = 0;

        for (int i = 0; i < (1 << n); i++) {
            if (Integer.bitCount(i) == rowCount) {
                goodMasksN[cntN++] = i;
            }
        }
        for (int i = 0; i < (1 << m); i++) {
            if (Integer.bitCount(i) == columnCount) {
                goodMasksM[cntM++] = i;
            }
        }

        int ans = n * m;

        int[] precalc = new int[(n / 2) * (m / 2) * 16];
        for (int i = 0; i < n / 2; i++) {
            for (int j = 0; j < m / 2; j++) {
                for (int it1 = 0; it1 <= 1; it1++) {
                    for (int it2 = 0; it2 <= 1; it2++) {
                        for (int it3 = 0; it3 <= 1; it3++) {
                            for (int it4 = 0; it4 <= 1; it4++) {
                                int curans = 0;
                                boolean h1 = it1 == 1;
                                boolean h2 = it2 == 1;
                                boolean v1 = it3 == 1;
                                boolean v2 = it4 == 1;
                                char val11 = A[i].charAt(j);
                                char val12 = A[i].charAt(m - j - 1);
                                char val21 = A[n - i - 1].charAt(j);
                                char val22 = A[n - i - 1].charAt(m - j - 1);
                                if (!h1 && !h2 && !v1 && !v2) {

                                } else if (h1 && !h2 && !v1 && !v2) {
                                    if (val11 != val12) {
                                        curans++;
                                    }
                                } else if (!h1 && h2 && !v1 && !v2) {
                                    if (val21 != val22) {
                                        curans++;
                                    }
                                } else if (!h1 && !h2 && v1 && !v2) {
                                    if (val11 != val21) {
                                        curans++;
                                    }
                                } else if (!h1 && !h2 && !v1 && v2) {
                                    if (val12 != val22) {
                                        curans++;
                                    }
                                } else if (h1 && h2 && !v1 && !v2) {
                                    if (val11 != val12) {
                                        curans++;
                                    }
                                    if (val21 != val22) {
                                        curans++;
                                    }
                                } else if (!h1 && !h2 && v1 && v2) {
                                    if (val11 != val21) {
                                        curans++;
                                    }
                                    if (val12 != val22) {
                                        curans++;
                                    }
                                } else if (h1 && !h2 && v1 && !v2) {
                                    if (val11 != val12 || val11 != val21) {
                                        curans++;
                                    }
                                } else if (h1 && !h2 && !v1 && v2) {
                                    if (val12 != val11 || val12 != val22) {
                                        curans++;
                                    }
                                } else if (!h1 && h2 && v1 && !v2) {
                                    if (val21 != val22 || val21 != val11) {
                                        curans++;
                                    }
                                } else if (!h1 && h2 && !v1 && v2) {
                                    if (val22 != val21 || val22 != val12) {
                                        curans++;
                                    }
                                } else {
                                    int cnt1 = 0;
                                    if (val11 == '1') {
                                        cnt1++;
                                    }
                                    if (val12 == '1') {
                                        cnt1++;
                                    }
                                    if (val21 == '1') {
                                        cnt1++;
                                    }
                                    if (val22 == '1') {
                                        cnt1++;
                                    }
                                    curans += min(cnt1, 4 - cnt1);
                                }
                                int pos = (i * m / 2 + j) * 16 + 1 * it1 + 2 * it2 + 4 * it3 + 8 * it4;
                                precalc[pos] = curans;
                            }
                        }
                    }
                }
            }
        }

        for (int iN = 0; iN < cntN; iN++) {
            int maskN = goodMasksN[iN];
            for (int iM = 0; iM < cntM; iM++) {
                int maskM = goodMasksM[iM];
                int curans = 0;
                for (int i = 0; i < n / 2; i++) {
                    for (int j = 0; j < m / 2; j++) {
                        boolean h1 = (maskN & (1 << i)) != 0;
                        boolean h2 = (maskN & (1 << (n - i - 1))) != 0;
                        boolean v1 = (maskM & (1 << j)) != 0;
                        boolean v2 = (maskM & (1 << (m - j - 1))) != 0;
                        int mask = 0;
                        if (h1) {
                            mask |= 1;
                        }
                        if (h2) {
                            mask |= 2;
                        }
                        if (v1) {
                            mask |= 4;
                        }
                        if (v2) {
                            mask |= 8;
                        }
                        curans += precalc[(((i * m >> 1) + j) << 4) + mask];
                    }
                }
                ans = min(ans, curans);
            }
        }

        return ans;
    }
}