import time
import random
from math import sqrt

def f(x, n):
    return sqrt(x * x * x + n * n * n)


def main():
    n = int(input())

    start = time.time()
    ans, cnt_loop = 0, 0

    while (time.time() - start) < 0.9:
        x = random.uniform(0, 1)
        ans += f(x, n)
        cnt_loop += 1

    ans /= cnt_loop

    print(ans)


if __name__ == "__main__":
    main()