h, w = map(int, input().split())
S = [list(map(int, input().split())) for _ in range(h)]
cum = [[0] * (w + 1) for _ in range(h + 1)]
for i in range(h):
    for j in range(w):
        cum[i + 1][j + 1] = cum[i + 1][j] + cum[i][j + 1] - cum[i][j] + S[i][j]


def f(i0, i1, j0, j1):
    return cum[i1][j1] - cum[i0][j1] - cum[i1][j0] + cum[i0][j0]


zz = [w] * (h + 1)
for i in range(h + 1):
    while zz[i] > 0 and f(i, h, zz[i] - 1, w) == 0:
        zz[i] -= 1

dp = [[1 << 30] * (w + 1) for _ in range(h + 1)]
dp[h][w] = 0

for i in range(h, -1, -1):
    for j in range(w, -1, -1):
        if i != h and f(i, i + 1, j, w) == 0:
            dp[i][j] = min(dp[i][j], dp[i + 1][j])
        if j != w and f(i, h, j, j + 1) == 0:
            dp[i][j] = min(dp[i][j], dp[i][j + 1])

        row = [0] * (h + 1)
        col = [0] * (w + 1)
        for i2 in range(i, h):
            row[i2 + 1] = row[i2] + int(f(i2, i2 + 1, j, w) > 0)
        for j2 in range(j, w):
            col[j2 + 1] = col[j2] + int(f(i, h, j2, j2 + 1) > 0)

        for i2 in range(i + 1, h + 1):
            j2 = max(j + 1, zz[i2])
            if j2 > w:
                continue
            tmp = dp[i2][j] + dp[i][j2] + (row[i2] * col[j2] - f(i, i2, j, j2))
            dp[i][j] = min(dp[i][j], tmp)

print(dp[0][0])