import java.math.BigInteger;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int N = scanner.nextInt();

		BigInteger max = BigInteger.ZERO;
		for (int i = 0; i < N; i++) {
			BigInteger upper = new BigInteger(String.valueOf(i));
			BigInteger lower = new BigInteger(String.valueOf(N - i));
			if (max.compareTo(upper.multiply(lower.add(BigInteger.ONE)).add(lower)) < 1) {
				max = upper.multiply(lower.add(BigInteger.ONE)).add(lower);
			}
		}

		System.out.println(max);
	}

}