import math
A, B, C, D, E, F = map(int, input().split())
if A == -1 or B == -1 :
	A *= -1
	B *= -1
	C *= -1
	D *= -1
	E *= -1
	F *= -1
ans = F - E + (C * C + D * D) / 4
ans = math.sqrt(ans)
print(ans)