source_code: 
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  
  /**
   *
   * @author Mostafa
   */
  public class Main {
      public static void main(String[] args) throws IOException {
          BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
          int n = Integer.parseInt(in.readLine());
          System.out.println((n/2) *3);
      }
  
  }
  