source_code: import java.io.PrintWriter;
  import java.util.Scanner;
  
  
  
  public class Solution {
  
      /**
       * @param args
       */
      public static void main(String[] args) {
          // TODO Auto-generated method stub
          Scanner in = new Scanner(System.in);
          PrintWriter out = new PrintWriter(System.out);
          int n=in.nextInt();
      
          out.print(n/2+n);
         
          out.close();
          in.close();
      }
  
  }
  