package main

import . "fmt"

func main() {
	var t int
	Scan(&t)
	for ; t>0; t-- {
		var a, b int
		Scan(&a,&b)
		if a == b {
			Println(0)
			continue
		}
		// B + X = c * v
		// A + X = v
		// B - A = (c - 1) * v
		d := b - a
		x := int(1e15)
		for v := 1; v*v <= d; v++ {
			if d % v != 0 {
				continue
			}
			c := d / v + 1
			if c * v - b == v - a && v - a >= 0 {
				x = min(x, v - a)
			}
			vv := d / v
			cc := d / vv + 1
			if cc * vv - b == vv - a && vv - a >= 0 {
				x = min(x, vv - a)
			}
		}
		if x < 1e15 {
			Println(x)
		} else {
			Println(-1)
		}
	}
}