import re
import sys

while True:
    try:
        card = input("Number: ").strip()  # Remove leading and trailing whitespaces
        if card.isdigit():
            break
    except:
        ValueError


if not (len(card) == 13 or len(card) == 15 or len(card) == 16):
    print("INVALID")
    quit()


cardNumber = int(card)
numLength = len(card)
id = int(card[0:4].splitlines()[0])


sum = multiply = 0

# Validate cardNumber with Luhn's Algorithm
while (cardNumber > 0):
    if (multiply):
        if (cardNumber % 10 * 2 > 9):
            n = cardNumber % 10 * 2
            while (n > 0):
                sum += int(n % 10)
                n = int(n / 10)
        else:
            sum += cardNumber % 10 * 2
        cardNumber = int(cardNumber / 10)
        multiply = 0
    else:
        sum += cardNumber % 10
        cardNumber = int(cardNumber / 10)
        multiply = 1
if (sum % 10 != 0):
    print("INVALID")
    quit()


if ((int(id / 100) == 34 or int(id / 100) == 37) and numLength == 15):
    print("AMEX")
    quit()

if ((int(id / 1000) == 4) and (numLength == 13 or numLength == 16)):
    print("VISA")
    quit()

if (((int(id / 100) >= 51 and int(id / 100) <= 55) or (id >= 2221 and id <= 2720)) and numLength == 16):
    print("MASTERCARD")
    quit()

else:
    print("INVALID")