def koma_sepp(n):
    """
    Take input integer n and return comma-separated string, separating
    1000s.

    >>> koma_sepp(131032047)
    '131,032,047'
    >>> koma_sepp(18781)
    '18,781'
    >>> koma_sepp(666)
    '666'

    """
    return '{:,}'.format(n)