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]


T=int(input())

for _ in range(T):
  A,B=map(int,input().split())
  divi = make_divisors(B-A)
  MIN = 1<<60
  for t in divi:
    X = (B-A)//t - A
    if X>=0:
      MIN = min(MIN, X)
  print(-1 if MIN==1<<60 else MIN)