def drop_prefix(s, prefix):
    """
    If s starts with prefix, drop it, otherwise return s.

    >>> print(drop_prefix('apabepa', 'ap'))
    abepa
    >>> print(drop_prefix('apabepa', 'cepa'))
    apabepa
    """
    if s.startswith(prefix):
        return s[len(prefix):]
    else:
        return s