def enumerate_divisors(n):
    divisors = set()
    for i in range(1, int(n**0.5) + 1):
        if n % i == 0:
            divisors.add(i)
            if i != n // i:
                divisors.add(n // i)
    return divisors
for _ in range(int(input())):
    a,b=map(int,input().split())
    if b%a==0:
        print(0)
    elif b//a==1:
        print(-1)
    else:
        T=True
        s=0
        if a<=10000:
            for i in range(10000):
                a+=1 
                b+=1 
                s+=1
                if b%a==0:
                    print(s)
                    T=False
        if T:
            x=b-a
            c=enumerate_divisors(x)
            for i in reversed(range(1,b//a)):
                if i in c:
                    print((b-a*(i+1))//i+s)
                    T=False
                    break
        if T:
            print(-1)