source_code: import java.io.*;
  
  public class N72A
  {
      StreamTokenizer in;
      PrintWriter out;
  
      int nextInt() throws IOException
      {
          in.nextToken();
          return (int) in.nval;
      }
  
      double nextDouble() throws IOException
      {
          in.nextToken();
          return in.nval;
      }
  
      public void init() throws Exception
      {
          boolean oj = System.getProperty("ONLINE_JUDGE") != null;
          Reader reader = oj ? new InputStreamReader(System.in) : new FileReader(new File("input.txt"));
          Writer writer = oj ? new OutputStreamWriter(System.out) : new FileWriter(new File("output.txt"));
          in = new StreamTokenizer(reader);
          out = new PrintWriter(writer);
      }
  
      public void solve() throws Exception
      {
          int n = nextInt();
          out.print(2*n - (n/2));
      }
  
      public void print() throws Exception
      {
          out.flush();
      }
  
      public void run() throws Exception
      {
          init();
          solve();
          print();
      }
  
      public static void main(String[] args) throws Exception
      {
          new N72A().run();
      }
  }