import java.util.*;
class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int W = N;
		long sum = 0;
		int i = 1;
		int j = 0;
		while(N>=3){
			N -= 2;
			sum += i;
			i++;
		}
		
		while(W>=3){
			W -= 2;
			sum += j;
			j++;
		}
		System.out.println(sum);
	}
}