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