package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func main() {
	sc.Buffer(make([]byte, 1000), 500000)
	sc.Split(bufio.ScanWords)
	n := nextInt()
	fmt.Println(float64(5*n*n*n) * (float64(3) + math.Sqrt(5)) / float64(12))
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func nextString() string {
	sc.Scan()
	return sc.Text()
}