from bisect import bisect_right
from typing import List
from math import floor, sqrt


def calc_positive_divisors(num: int) -> List[int]:
    small_divisors = []
    large_divisors = []
    for n in range(1, floor(sqrt(num)) + 1):
        if num % n == 0:
            small_divisors.append(n)
            large_divisors.append(num // n)
    if small_divisors[-1] == large_divisors[-1]:
        large_divisors.pop()
    divisors = small_divisors + list(reversed(large_divisors))
    return divisors


def main():
    for _ in range(int(input())):
        A, B = map(int, input().split())
        if B % A == 0:
            print(0)
            continue
        if A * 2 > B:
            print(-1)
            continue
        multiple = B // A

        divisors = calc_positive_divisors(B - A)
        idx = bisect_right(divisors, multiple - 1)
        print((B - (divisors[idx - 1] + 1) * A) // divisors[idx - 1])

        # (B+X) = M(A+X)
        # B-MA = (M-1)X
        # X = (B-MA)/(M-1)
        # X = (B-A-(M-1)A)/(M-1)


if __name__ == "__main__":
    main()