source_code: import java.math.BigInteger;
  import java.util.*;
  
  /**
   * Created by IntelliJ IDEA.
   * User: piyushd
   * Date: 4/13/11
   * Time: 8:07 PM
   * To change this template use File | Settings | File Templates.
   */
  public class TaskA1 {
  
      void run(){
          int n = nextInt();
  
          int ans = 2 * n - (n / 2);
          System.out.println(ans);
      }
  
      int nextInt(){
          try{
              int c = System.in.read();
              if(c == -1) return c;
              while(c != '-' && (c < '0' || '9' < c)){
                  c = System.in.read();
                  if(c == -1) return c;
              }
              if(c == '-') return -nextInt();
              int res = 0;
              do{
                  res *= 10;
                  res += c - '0';
                  c = System.in.read();
              }while('0' <= c && c <= '9');
              return res;
          }catch(Exception e){
              return -1;
          }
      }
  
      long nextLong(){
          try{
              int c = System.in.read();
              if(c == -1) return -1;
              while(c != '-' && (c < '0' || '9' < c)){
                  c = System.in.read();
                  if(c == -1) return -1;
              }
              if(c == '-') return -nextLong();
              long res = 0;
              do{
                  res *= 10;
                  res += c-'0';
                  c = System.in.read();
              }while('0' <= c && c <= '9');
              return res;
          }catch(Exception e){
              return -1;
          }
      }
  
      double nextDouble(){
          return Double.parseDouble(next());
      }
  
      String next(){
          try{
              StringBuilder res = new StringBuilder("");
              int c = System.in.read();
              while(Character.isWhitespace(c))
                  c = System.in.read();
              do{
                  res.append((char)c);
              }while(!Character.isWhitespace(c=System.in.read()));
              return res.toString();
          }catch(Exception e){
              return null;
          }
      }
  
      String nextLine(){
          try{
              StringBuilder res = new StringBuilder("");
              int c = System.in.read();
              while(c == '\r' || c == '\n')
                  c = System.in.read();
              do{
                  res.append((char)c);
                  c = System.in.read();
              }while(c != '\r' && c != '\n');
              return res.toString();
          }catch(Exception e){
              return null;
          }
      }
  
      public static void main(String[] args){
          new TaskA1().run();
      }
  
  
  
  }
  