def only_main(compound: str):
    """Convert a splitted compound into a compound only split into
    a main compound and its satelite e.g. fietsen_stalling_pas ->
    fietsenstalling_pas

    Args:
        compound (str): an underscore splitted compound
    """
    splitted = compound.split("_")
    if len(splitted) == 1:
        return splitted[0]
    return "".join(splitted[:-1]) + "_" + splitted[-1]