T=int(input())
for _ in range(T):
  a,b=map(int,input().split())
  if b%a==0:
    print(0)
    continue
  b=b-a
  ans=10**10
  for i in range(1,int(b**0.5)+1):
    if b%i==0:
      if i>a:
        ans=min(ans,i-a)
      if (b//i)>a:
        ans=min(ans,b//i-a)
  print(ans if ans<10**10 else -1)