source_code: import java.util.*;
  import java.io.*;
  public class C72A{
      static BufferedReader br;
      public static void main(String args[])throws Exception{
          br=new BufferedReader(new InputStreamReader(System.in));
          long n=toLong();
          long res=n+n/2;
          System.out.println(res);
  
  
      }
  
  
      /****************************************************************/
      public static int[] toIntArray()throws Exception{
         String str[]=br.readLine().split(" ");
         int k[]=new int[str.length];
         for(int i=0;i<str.length;i++){
              k[i]=Integer.parseInt(str[i]);
         }
         return k;
      }
      public static int toInt()throws Exception{
         return Integer.parseInt(br.readLine());
      }
      public static long[] toLongArray()throws Exception{
         String str[]=br.readLine().split(" ");
         long k[]=new long[str.length];
         for(int i=0;i<str.length;i++){
              k[i]=Long.parseLong(str[i]);
         }
         return k;
      }
      public static long toLong()throws Exception{
         return Long.parseLong(br.readLine());
      }
      public static double[] toDoubleArray()throws Exception{
         String str[]=br.readLine().split(" ");
         double k[]=new double[str.length];
         for(int i=0;i<str.length;i++){
              k[i]=Double.parseDouble(str[i]);
         }
         return k;
      }
      public static double toDouble()throws Exception{
         return Double.parseDouble(br.readLine());
      }
      public static String toStr()throws Exception{
         return br.readLine();
      }
      public static String[] toStrArray()throws Exception{
         String str[]=br.readLine().split(" ");
         return str;
      }
      /****************************************************************/
  
  }
  