source_code: /*
   * 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++];
         }
      }