import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
public class Main {

	 public static void main(String[] args) {
	      BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
	      try {
	    	  BigInteger num = BigInteger.valueOf(Long.parseLong(stdReader.readLine()));
	    	  BigInteger up = num.divide(BigInteger.valueOf(2));
	    	  BigInteger down = num.subtract(up);
	    	  BigInteger ans = up.multiply(down.add(BigInteger.valueOf(1))).add(down);
	    	  System.out.println(ans);
	      } catch (IOException e) {
			e.printStackTrace();
	      }
	}
}