#a = primary divisor -> next quotient
#q = quotient -> remainder
def gcd(q, a):
    while q >= a:
        q = q - a
    if q != 0:
        if gcd(a, q) == 0:
            return q
        else:
            return gcd(a, q)
    else:
        return q
print(gcd(20, 3))