The hero of our story, Valera, and his best friend Arcady are still in school, and therefore they spend all the free time playing turn-based strategy "GAGA: Go And Go Again". The gameplay is as follows. 

There are two armies on the playing field each of which consists of n men (n is always even). The current player specifies for each of her soldiers an enemy's soldier he will shoot (a target) and then all the player's soldiers shot simultaneously. This is a game world, and so each soldier shoots perfectly, that is he absolutely always hits the specified target. If an enemy soldier is hit, he will surely die. It may happen that several soldiers had been indicated the same target. Killed soldiers do not participate in the game anymore. 

The game "GAGA" consists of three steps: first Valera makes a move, then Arcady, then Valera again and the game ends. 

You are asked to calculate the maximum total number of soldiers that may be killed during the game. 

Input

The input data consist of a single integer n (2 ≤ n ≤ 108, n is even). Please note that before the game starts there are 2n soldiers on the fields. 

Output

Print a single number — a maximum total number of soldiers that could be killed in the course of the game in three turns.

Examples

Input

2


Output

3


Input

4


Output

6

Note

The first sample test:

1) Valera's soldiers 1 and 2 shoot at Arcady's soldier 1.

2) Arcady's soldier 2 shoots at Valera's soldier 1.

3) Valera's soldier 1 shoots at Arcady's soldier 2.

There are 3 soldiers killed in total: Valera's soldier 1 and Arcady's soldiers 1 and 2.
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author Saransh
 */
import java.io.*;
import java.util.*;
import java.math.*;
import java.lang.*;


public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        try
        {
            Parserdoubt pd=new Parserdoubt(System.in);
            //BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            int n=pd.nextInt();
            PrintWriter pw=new PrintWriter(System.out);
            pw.println((n*3)/2);
            pw.flush();
        }
        catch(Exception e)
        {}

    }

}


class Parserdoubt
    {
       final private int BUFFER_SIZE = 1 << 17;

       private DataInputStream din;
       private byte[] buffer;
       private int bufferPointer, bytesRead;

       public Parserdoubt(InputStream in)
       {
          din = new DataInputStream(in);
          buffer = new byte[BUFFER_SIZE];
          bufferPointer = bytesRead = 0;
       }
       public String nextString() throws Exception
       {
           StringBuffer sb=new StringBuffer("");
           byte c = read();
           while (c <= ' ') c = read();
           do
           {
               sb.append((char)c);
               c=read();
           }while(c>' ');
           return sb.toString();
       }
       public char nextChar() throws Exception
       {
           byte c=read();
           while(c<=' ') c= read();
           return (char)c;
       }
       public int nextInt() throws Exception
       {
          int ret = 0;
          byte c = read();
          while (c <= ' ') c = read();
          boolean neg = c == '-';
          if (neg) c = read();
          do
          {
              ret = ret * 10 + c - '0';
             c = read();
          } while (c > ' ');
          if (neg) return -ret;
          return ret;
       }
       public long nextLong() throws Exception
       {
          long ret = 0;
          byte c = read();
          while (c <= ' ') c = read();
          boolean neg = c == '-';
          if (neg) c = read();
          do
          {
              ret = ret * 10 + c - '0';
             c = read();
          } while (c > ' ');
          if (neg) return -ret;
          return ret;
       }
       private void fillBuffer() throws Exception
       {
          bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
          if (bytesRead == -1) buffer[0] = -1;
       }

       private byte read() throws Exception
       {
          if (bufferPointer == bytesRead) fillBuffer();
          return buffer[bufferPointer++];
       }
    }