def next_cell(board, current):
    """
    Get next cell in board after current
    :param board: matrix
    :param current: tuple (matrix index)
    :return: tuple(matrix index) or None if not exists
    """
    for row in range(current[0], len(board)):
        for col in range(current[1], len(board)):
            if board[row][col] == 0:
                return (row, col)
    for row in range(len(board)):
        for col in range(len(board)):
            if board[row][col] == 0:
                return (row, col)
    return None