def return_subset_number(pedigree):

    """
    Find out how many founders there are in the given file.
    """

    founder = 0
    with open(pedigree, 'r') as filein:
        for lines in filein:
            line = lines.rstrip().split()
            if line[2] == "0" and line[3] == "0": founder += 1

    return founder