for _ in range(int(input())):
    a,b = map(int,input().split())
    if a==b: print(0); continue
    if 2*a>b: print(-1); continue
    c = b-a; d = []
    for i in range(1,int(c**0.5)+1):
        if c%i==0: d += [i,c//i]
    for v in sorted(d):
        if v>=a: print(v-a); break