from sets import *

def sd(a,b,c):
	assert a != 0
	S = set()
	Delta = b**2-4*a*c
	if Delta >= 0:
		r = Delta**0.5
		S.add((-b-r)/(2*a))
		S.add((-b+r)/(2*a))
	return S

print sd(1,-2,1)