import math
	

	

		values = list(map(int,input().split()))
	

	

		X = values[0]
	

	

		Y = values[1]
	

	

		N = math.sqrt(2*(X+Y)+1/4)-1/2
	

	

		n = int(math.sqrt(2*Y+1/4)-1/2)
	

	

		ret = -1
	

	

		if int(N) == N:
	

	

		ret = int(N-n)
	

	

		print(ret)