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

int main() {
    int h, w;
    cin >> h >> w;
    vector<vector<int>> S(h, vector<int>(w));
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            cin >> S[i][j];
        }
    }

    vector<vector<int>> cum(h + 1, vector<int>(w + 1, 0));
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            cum[i + 1][j + 1] = cum[i + 1][j] + cum[i][j + 1] - cum[i][j] + S[i][j];
        }
    }

    auto f = [&](int i0, int i1, int j0, int j1) -> int { return cum[i1][j1] - cum[i0][j1] - cum[i1][j0] + cum[i0][j0]; };

    vector<int> zz(h + 1, w);
    for (int i = 0; i <= h; i++) {
        while (zz[i] > 0 && f(i, h, zz[i] - 1, w) == 0) zz[i]--;
    }

    vector<vector<int>> dp(h + 1, vector<int>(w + 1, 1 << 30));
    dp[h][w] = 0;

    for (int i = h; i >= 0; i--) {
        for (int j = w; j >= 0; j--) {
            if (i != h && f(i, i + 1, j, w) == 0) dp[i][j] = min(dp[i][j], dp[i + 1][j]);
            if (j != w && f(i, h, j, j + 1) == 0) dp[i][j] = min(dp[i][j], dp[i][j + 1]);

            vector<int> row(h + 1, 0);
            vector<int> col(w + 1, 0);
            for (int i2 = i; i2 < h; i2++) row[i2 + 1] = row[i2] + (f(i2, i2 + 1, j, w) > 0 ? 1 : 0);
            for (int j2 = j; j2 < w; j2++) col[j2 + 1] = col[j2] + (f(i, h, j2, j2 + 1) > 0 ? 1 : 0);

            for (int i2 = i; i2 <= h; i2++) {
                int j2   = max(j + 1, zz[i2]);
                int tmp  = dp[i2][j] + dp[i][j2] + row[i2] * col[j2] - f(i, i2, j, j2);
                dp[i][j] = min(dp[i][j], tmp);
            }
        }
    }

    cout << dp[0][0] << endl;
}