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

public class Main {
	public static void main(String[] args) {
	      BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
	      try {
	    	  long N = Long.parseLong(stdReader.readLine());
	    	  long sum = 0;
	    	  long index = 0;
	    	  while(N >=3){
	    		  sum += index*2+1;
	    		  index++;
	    		  N -= 2;
	    	  }
	    	  System.out.println(sum);
	    	  } catch (IOException e) {
			e.printStackTrace();
	      }
	}	
}