def gcd(a, b):
    r = a % b
    if r == 0:
        return b
    else:
        return gcd(b, r)

print("gcd of 12 and 8 is", gcd(12, 8))
print("gcd of 10 and 5 is", gcd(10, 5))
print("gcd of 20 and 24 is", gcd(20, 24))