def gcd(a, b):
    while b:      
        a, b = b, a % b
    return a

def lcm(a, b):
    return a * b // gcd(a, b)

a, b = sorted(map(int, raw_input().split()))
if(a == b):
    print 1
elif(a < b-a):
    print((b-a) % a)
else:
    print b-a - a%(b-a)