import math
A, B = map(int, raw_input().split())
divisors = []
for i in range(1, int(math.sqrt(A+B))+1):
	if (A+B)%i == 0: divisors.append(i)
N = len(divisors)
for i in range(0, N):
	if (A+B)/divisors[i] not in divisors: divisors.append((A+B)/divisors[i])
divisors.sort()

min = -1
for i in range(0, len(divisors)):
	if A != divisors[i] and B != divisors[i]:
		if (B+divisors[i])%A == 0 and (A+divisors[i])%B == 0:
			min = divisors[i]
			break
print min