for _ in range(int(input())):
    a, b = map(int, input().split())
    d = b - a
    if d == 0:
        print(0)
        continue
    factors = []
    for i in range(1, int(d**0.5) + 1):
        if d % i == 0:
            factors.append(i)
            factors.append(d // i)
    factors.sort()
    ans = -1
    for f in factors:
        if f >= a:
            ans = f - a
            break
    print(ans)