package main

import (
	"fmt"
)

func main() {
	var l int

	fmt.Scanln(&l)

	a := (l - 1) / 2
	b := (l - 2) / 2

	ac := a * (a + 1) / 2
	bc := b * (b + 1) / 2
	fmt.Println(ac + bc)
}