def Divisors(N):
    divisors=[]
    for i in range(1,N+1):
        if i**2>=N:
            break
        elif N%i==0:
            divisors.append(i)
    if i**2==N:
        divisors+=[i]+[N//i for i in divisors[::-1]]
    else:
        divisors+=[N//i for i in divisors[::-1]]
    return divisors

T=int(input())
for t in range(T):
    A,B=map(int,input().split())
    if A==B:
        ans=0
    else:
        inf=1<<60
        ans=inf
        for d in Divisors(B-A):
            if d>=A:
                ans=min(ans,d-A)
        if ans==inf:
            ans=-1
    print(ans)