package main

import (
	"fmt"
	"math"
)

func main() {
	var d int
	fmt.Scanf("%d", &d)
	var a int
	a = int(math.Sqrt(float64(d) / 2.0))
	ans := 0
	for dx := -10; dx <= 10; dx++ {
		for dy := -10; dy <= 10; dy++ {
			x := a + dx
			y := a + dy
			if x < 0 {
				continue
			}
			if y < 0 {
				continue
			}
			if 2*(x+y) > d {
				continue
			}
			if ans < x*y {
				ans = x * y
			}
		}
	}
	fmt.Println(ans)
}