URI_1211.py

while True:
    try:
        num = int(input() or 0)
    except EOFError:
        num = 0

    if not num:
        break

    chars_saved = 0
    last_phone = None
    phone_list = [input() for _ in range(num)]
    phone_list.sort()

    for phone in phone_list:
        if last_phone is None:
            last_phone = phone
            continue
        
        # compara as strings
        for new_phone_char, last_phone_char in zip(phone, last_phone):
            if new_phone_char == last_phone_char:
                chars_saved += 1
            else:
                break

        last_phone = phone
    print(chars_saved)