'''
The area of an equilateral triangle is ¼(√3a2) where "a" represents a side of the triangle. You are provided with the side "a". Find the area of the equilateral triangle.

Input Description:
The side of an equilateral triangle is provided as the input.

Output Description:
Find the area of the equilateral triangle and print the answer up to 2 decimal places after rounding off.

Sample Input :
20
Sample Output :
173.21'''
side = float(input())
area = (1 * (3 ** 0.5) * (side * side))/4
print(round(area,2))
