import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Yukicoder70 {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		long n = Integer.parseInt(br.readLine());
		long max = -1;
		
		for (int i = 1; i < n; i++) {
			max = Math.max(max, i * (n - i + 1) + n - i);
		}
		System.out.println(max);

	}

}