def gcd(num1, num2):
    '''returns the GCD of num1 and num2'''
    x = max(num1, num2) # larger
    y = min(num1, num2) # smaller
    r = x % y
    while r != 0:
        x = y
        y = r
        r = x % y
    return y

###### One-and-a-half Loop Version ######

num1 = input("Input a number: ")
num2 = input("Input another number: ")
while num1 != 'quit' and num2 != 'quit':
    result = gcd(int(num1), int(num2))
    print("GCD is " + str(result))    
    num1 = input("Input a number: ")
    num2 = input("Input another number: ")
print("Bye!")

##### Alternate Boolean Flag Version #######

finished = False
while not finished:
    num1 = input("Input a number: ")
    num2 = input("Input another number: ")
    if num1 == "quit" or num2 == "quit":
        finished = True
    else:
        result = gcd(int(num1), int(num2))
        print("GCD is " + str(result))
print("Bye!")

def read_words():
    '''prompt the user for a list of words (one at a time),
    then return the list'''
    word_list = []
    next_word = input("Word: ")
    while next_word != '':
        word_list.append(next_word)
        next_word = input("Word: ")
    return word_list