with open("27-B.txt", "r", encoding="utf-8") as f:
    data = f.readlines()
    participators = [list() for i in range(5000)]
    for index, line in enumerate(data):
        if not index:
            n = int(line.split()[1])
            continue
        number, a, b, c = map(int, line.split())
        participators[number].append(max([a, b, c]))

    participators = list(filter(lambda x: len(x) > n, participators))
    participators = sorted(list(map(lambda x: sum(x) / len(x), participators)))
    print(participators[-1] - participators[0])