S = input
R = range
P = print
def I(): return int(S())
def M(): return map(int, S().split())
def L(): return list(M())
def O(): return list(map(int, open(0).read().split()))
def yn(b): print("Yes" if b else "No")
biga = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
smaa = "abcdefghijklmnopqrstuvwxyz"

def make_divisors(n):
    lower_divisors , upper_divisors = [], []
    i = 1
    while i*i <= n:
        if n % i == 0:
            lower_divisors.append(i)
            if i != n // i:
                upper_divisors.append(n//i)
        i += 1
    return lower_divisors + upper_divisors[::-1]

for _ in R(I()):
	a, b = M()
	if a == b:
		print(0)
		continue
	c = 10 ** 15
	# b - a の約数を全探索
	for i in make_divisors(b - a):
		if i >= a and (b + i - a) % (a + i - a) == 0:
			c = min(c, i - a)
	print(c if c < 10 ** 15 else -1)