#ax,ay,az=map(int, input().split())
#bx,by,bz=map(int, input().split())
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 i in range(T):
  a,b=map(int, input().split())
  A=make_divisors(b-a)
  ans=-1
  for aa in A[::-1]:
    if aa>=a:
      ans=aa-a 
  print(ans)