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

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader =new BufferedReader(new InputStreamReader(System.in));
        long L = Long.parseLong(reader.readLine());
        long n = (L-1)/2;
        System.out.println(n*n);
    }
}