/*
L3 = 1
Ln = Ln-1 + n - 2
 */

import java.util.Scanner;

class Test {
	public static int aba(int n) {
		if(n == 3) {
			return 1;
		} else {
			return aba(n-1) + n - 2;
		}
	}

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

		int ans = aba(l);

		System.out.println(ans);
	}
}