Контрольная. Задание 2

from collections import Counter


if __name__ == "__main__":
    pairs = []

    while True:
        line = input()
        if line == "0": break
        first_part, second_part = line.split(", ")
        authors = first_part.split()
        temi = second_part.split()

        for a in authors:
            for t in temi:
                pairs.append((a, t))

    counter = Counter(pairs)
    maximum = counter.most_common(1)[0][1]

    for pair in counter.most_common():
        if pair[1] == maximum:
            print(pair[0])