from math import isqrt
def divisors(n):
  r = isqrt(n-1)+1
  small, large = [], []
  for i in range(1, r):
    if n%i == 0:
      small.append(i)
      large.append(n//i)
  if r**2 == n: small.append(r)
  return small + large[::-1]

T = int(input())
for _ in range(T):
  A, B = map(int, input().split())
  if A == B:
  	print(0)
  	continue
  D = divisors(B - A)
  for d in D:
    if d >= A:
      print(d - A)
      break
  else: print(-1)