from math import*
n = int(input())
c = 0
d = 0
e = 3
aux = -1
while(c<n):
	if(c==0):
		e = e
	else:
		e = e + (aux * (4/(d*(d+1)*(d+2))))
	if(aux==1):
		aux=-1
	else:
		aux=1
	c = c+1
	d = d+2

print(round(e, 8))