from cs50 import get_int

def main():
    while True:
        num=get_int("Number: ")
        if num > 0:
            break

    checksum(num)

def checksum(n):
    s1=s2=b=0
    i=1

    while n>0:
        digit=n%10

        if i%2==0:
            d=digit*2

            if d<10:
                s1+=d

            else:
                s1+=d%10
                d/=10
                s1+=d

        else:
            s2+=digit

        n/=10

        if n>=10:
            a=n
        b+=1

        i+=1

    s=s1+s2

    if s%10==0:
        if b==15 and (a==34 or a==37):
            print("AMEX")

        elif b==16:
            if a in range(51,52):
                print("MASTERCARD")

            elif (a/10)==4:
                print("VISA")

    else:
        print("INVALID")

if __name__ == "__main__":
    main()