import java.util.Scanner;


public class Main_yukicoder71 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        long max = 0;
        for (int i = 1; i < n; i++) {
        	max = Math.max(max, (long)(i + 1) * (n - i + 1) - 1);
        }

		System.out.println(max);
        
        sc.close();
    }
}