from decimal import Decimal, getcontext

# Set a high precision to handle the floating-point calculations accurately
getcontext().prec = 100

L = int(input())
sqrt3 = Decimal(3).sqrt()
area = (Decimal(L) ** 2) * sqrt3 / Decimal(36)

# Convert to a string and format to remove trailing zeros
formatted_area = format(area, 'f').rstrip('0').rstrip('.') if '.' in format(area, 'f') else format(area, 'f')

print(formatted_area)