from math import sqrt
N = int(input())
N3 = N*N*N

def f(x):
    return sqrt(x*x*x + N3)
S = 0
a = f(0)
for i in range(50000):
    dx = 1 / 50000
    b = f((i+1)*dx)
    s = ((a+b)*dx) / 2
    S += s
    a = b

print(S)