from collections import Counter


def read_companies(file):
    with open(file) as f:
        data = f.read()
    return data.strip().split()

files = ["ilon.txt", "bill.txt", "sasha.txt"]
all_companies = Counter(sum(map(read_companies, files)))

print(len([company for company, count in all_companies.most_common() if count >= 2]))