from cs50 import get_int

credit = get_int("Number:")
na = int(str(credit)[:2])
naa = int(na /10)
le = len(str(credit))
sum = 0
while credit > 0 :
    n1 = int(credit%10)
    credit = credit/10
    n2 = int(credit%10 *2)
    credit = credit/10
    n2 = int(n2/10 +n2%10)
    sum = n1 +n2 + sum
if sum%10 == 0 :
    if (na == 34 or na ==37) and (le ==15):
        print("AMEX")
    elif (na ==51 or na ==52 or na ==53 or na==54 or na ==55) and (le==16) :
        print("MASTERCARD")
    elif (naa %10 ==4) and (le==13 or le==16):
        print("VISA")
    else :
        print("INVALID")
else :
    print("INVALID")