from decimal import Decimal, getcontext

n = int(input())
getcontext().prec = 200  # Set a high precision to ensure accuracy

sqrt5 = Decimal(5).sqrt()
coeff = (Decimal(5) * (Decimal(3) + sqrt5)) / Decimal(12)
volume = coeff * (Decimal(n) ** 3)

# Format the output to 20 decimal places
print("{0:.20f}".format(volume))