n = int(input())

def f(x):
    return (x * x * x + n * n * n) ** 0.5

N = 10 ** 5

a = 0
b = 1
h = (b-a)/N

S = (h/3) * sum((f(h*i) + 4*f(h*(i+1)) + f(h*(i+2))) for i in range(0,N-1, 2))

print(S)