N = int(input())

if N == 0:
  print(0.4)

# テイラー展開
else:
  a = 0.5
  c = 1
  n = 1
  ans = 1
  i = 1
  for j in range(60):
    c *= a
    a -= 1
    c /= i
    n *= N * N * N
    res = (3 * i + 1) * n
    ans += c / res
    i += 1
    if n > 10 ** 18:
      break
  print(ans * (N ** 1.5))