import java.io.*;
import java.util.*;


public class Main_yukicoder831_1 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int n = sc.nextInt();
		
		if (n == 1) {
			pr.println(0);
			return;
		}
		
		Deque<Integer> q = new ArrayDeque<>(n);
		for (int i = 1; i < n; i++) {
			q.add(i);
		}
		
		Deque<Integer> ans = new ArrayDeque<>(n);
		ans.add(0);

		while (!q.isEmpty()) {
			int last = ans.getLast();
			int first = ans.getFirst();
			int large = q.getLast();
			int small = q.getFirst();
			
			int diff1 = Math.abs(large - last);
			int diff2 = Math.abs(large - first);
			int diff3 = Math.abs(small - last);
			int diff4 = Math.abs(small - first);
			if (diff1 >= diff2 && diff1 >= diff3 && diff1 >= diff4) {
				ans.addLast(large);
				q.removeLast();
			} else if (diff2 >= diff1 && diff2 >= diff3 && diff2 >= diff4) {
				ans.addFirst(large);
				q.removeLast();
			} else if (diff3 >= diff1 && diff3 >= diff2 && diff3 >= diff4) {
				ans.addLast(small);
				q.removeFirst();
			} else {
				ans.addFirst(small);
				q.removeFirst();
			}
		}
		
		List<Integer> list = new ArrayList<>(ans);
		long cost = 0;
		for (int i = 0; i < n; i++) {
			int ii = list.get(i) + 1;
			int jj = list.get((i + 1) % n) + 1;
			cost += (long)ii * jj + jj - ii;
		}

//		pr.println(list);
		pr.println(cost);
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);
			
		solve();
			
		pr.close();
		sc.close();
	}

	static class Printer extends PrintWriter {
		Printer(OutputStream out) {
			super(out);
		}
	}
}