source_code: import java.io.*;
  import java.util.*;
  import java.math.*;
  import java.lang.*;
  import java.text.*;
  
  
  public class Main
  {
  
  
  
      public static void main(String[] args)
   {
  
  Scanner sc = new Scanner(System.in);
  int T =sc.nextInt();
  
  int t =T/2;
  System.out.println(t*3);
  
  
  }
  
  }