#Find the area of the equilateral triangle
#header file for sqrt function
import math
#function to find the area
def equilateral_triangle(s):
#formula to find the area of a equilateral triangle
  a=(math.sqrt(3)/4)*(s*s)
#return the value of a
  return a
#get the side of a triangle from the user 
s=int(input())
#call the function 
r=equilateral_triangle(s)
e=round(r,2)
print(e)
