import sys
input = sys.stdin.readline

T=int(input())
for tests in range(T):
    A,B=map(int,input().split())

    if A==B:
        print(0)
        continue

    u=B-A
    L=[]

    for i in range(1,10**5):
        if u%i==0:
            L.append(i)
            L.append(u//i)

    ANS=1<<63

    for l in L:
        if l>=A:
            ANS=min(ANS,l-A)

    if ANS==1<<63:
        ANS=-1
        print(ANS)
    else:
        print(ANS)