def divisors(n):
  small, large = [], []
  i = 1
  while i**2 < n:
    if n%i == 0:
      small.append(i)
      large.append(n//i)
    i += 1
  if i**2 == n: small.append(i)
  return small + large[::-1]

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