"""Euclid's GCD by repeated subtraction."""

def gcd(a, b):
    while a != b:
        if a > b:
            a = a - b
        else:
            b = b - a
    return a


if __name__ == "__main__":
    for a, b in [(48, 18), (100, 75), (17, 5), (12, 12)]:
        print(f"gcd({a}, {b}) = {gcd(a, b)}")