pi

pi.py

from decimal import getcontext  , Decimal
from math import sqrt

def root(a):
	x=Decimal(sqrt(a))
	y=Decimal(0)
	while(abs(x-y)>Decimal(0.1)**(getcontext().prec-1)):
		x,y=x-(x*x-a)/(2*x),x
	return x

def pi(keta):
	getcontext().prec=keta
	a=Decimal(1)
	b=a/root(2)
	t=a/4
	p=a
	x=Decimal(3)
	y=a
	while(abs(x-y)>Decimal(0.1)**(getcontext().prec-1)):
		aa=(a+b)/2
		b=root(a*b)
		t=t-p*(a-aa)**2
		p=p*2
		a=aa
		x,y=((a+b)*(a+b))/(4*t),x
	return x
	

def main():
	print pi(input())

if __name__=="__main__":
	main()