import sys, time, random
from collections import deque, Counter, defaultdict
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 61 - 1
mod = 998244353

def solve():
    a, b = mi()
    #あるmが存在して，m(a + x) = b + xを満たすxが存在するか
    #ma + mx = b + x
    #mx - x = b - ma
    #x(m - 1) = b - ma
    #x = (b - ma) / (m - 1)
    #x = (b - a - (m - 1)a) / (m - 1)
    #x = (b - a) / (m - 1) - a
    ans = inf
    if a == b:
        print(0)
        return
    if b - 2 * a >= 0:
        k = b - a
        for v in range(1, k + 1):
            if v * v > k:
                break
            if k % v == 0:
                x = k // v
                if x > 0 and k // x - a >= 0 and b - x * a >= 0:
                    ans = min(ans, k // x - a)
                x = v
                if x > 0 and k // x - a >= 0 and b - x * a >= 0:
                    ans = min(ans, k // x - a)
        print(ans if ans < inf else -1)   
    else:
        print(-1)
    
    
    
    
for _ in range(ii()):
    solve()