for j in range(int(input())):
	a,b=map(int,input().split())
	div=[]
	g=b-a
	if g==0:
	  print(0)
	  continue
	for i in range(1,int(g**0.5)+1):
		if g%i==0:
			div.append(i)
			div.append(g//i)
	div.sort()
	for i in div:
	  if i>=a:
	    if (b-a+i)%i==0:
	      print(i-a)
	      break
	else:
	  print(-1)