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

public class Main {
	public static void main(String[] args) {
		BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

		try {
			long line = Long.parseLong(buff.readLine());

			long ans = line - 2;
			long pro = line - 2;


			for(int i = 5; i <= line; i += 2){
				pro -= 2;
				ans += pro;
			}

			System.out.println(ans);

		} catch (NumberFormatException e) {
			e.getStackTrace();
		} catch (IOException e) {
			e.getStackTrace();
		} catch (Exception e) {
			e.getStackTrace();
		}
	}
}