def get_filename_in_second_line(cpp_txt):
    """
    From the second line of cpp_txt, get the filename

    Expected input argument:
    // ```
    // Begin file_name.cpp
    // ...

    Expected output argument in this case:
    file_name.cpp
    """

    result = ""

    for line in cpp_txt.splitlines():
        if line.strip().lower().startswith('//'):
            # ignore if too short
            if 2 < len(line.lower().split()):
                # If second word is 'begin'
                if 'begin' == line.lower().split()[1]:
                    result = line.lower().split()[-1]
                    break

    return result