def gcd (num1, num2):
    ''' greatest common divisor '''
    while num2 != 0:
        if num1 > num2:
            num1 = num1 - num2
        else:
            num2 = num2 - num1
    return num1

def main():
    print("Finding greatest common divisor ")
    n1 = int(input("Enter first number "))
    while n1 != 0:
        n2 = int(input("Enter second number "))
        print(gcd(n1, n2))
        n1 = int(input("Enter first number "))
        

main()