def binary_matrix(A):
    row, col = len(A), len(A[0])
    dp = [[0 for j in range(col)] for i in range(row)]
    for i in range(row):
        dp[i][0] = A[i][0]
    for j in range(col):
        dp[0][j] = A[0][j]
    for i in range(1, row):
        for j in range(1, col):
            if A[i][j] == 0:
                dp[i][j] = 0
            else:
                dp[i][j] = 1 + min(dp[i - 1][j], dp[i][j - 1], dp[i - 1][j - 1])
    max_ele = dp[0][0]
    max_i, max_j = 0, 0
    for i in range(row):
        for j in range(col):
            if max_ele < dp[i][j]:
                max_ele = dp[i][j]
                max_i, max_j = i, j

    k = max_ele
    return k


M = [[0, 1, 1, 0, 1],
     [1, 1, 0, 1, 0],
     [0, 1, 1, 1, 0],
     [1, 1, 1, 1, 0],
     [1, 1, 1, 1, 1],
     [0, 0, 0, 0, 0]]

print(binary_matrix(M))