#!/usr/bin/python

import math

delta=0.0001
lower_bound = -1.0
upper_bound =  1.0
area = 0

def f(x): return math.sqrt(1.0-x*x)

x=lower_bound
while (x<=upper_bound):
	# Calculate the area of a rectangular strip...
	area = area + (delta * f(x))
	# ... and add it to the running total.
	x = x + delta

total_area = 2*area
print total_area