import sys
input = sys.stdin.readline

def div(n):
    if n <= 0:
        return []
    S = set()
    i = 1
    while i * i <= n:
        if n % i == 0:
            S.add(i)
            S.add(n//i)
        i += 1
    return sorted(list(S))

def ceil(A, d):
    return (A + d - 1)//d * d - A


T = int(input())
inf = 10 ** 18
for _ in range(T):
    A, B = map(int, input().split())
    if B % A == 0:
        print(0)
        continue
    ans = inf
    for d in div(B - A):
        x = ceil(A, d)
        if (B + x) % (A + x) == 0:
            ans = min(ans, x)
            
    print(ans) if ans != inf else print(-1)