source_code: import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.io.OutputStreamWriter;
  import java.io.PrintWriter;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  import java.util.StringTokenizer;
  
  /**
   * @author abashkin
   */
  public class Solution implements Runnable {
  
      public static void main(String[] args) {
          new Thread(new Solution()).start();
      }
  
      public void run() {
          try{
              br = new BufferedReader(new InputStreamReader(System.in));
              pw = new PrintWriter(new OutputStreamWriter(System.out));
              solve();
              pw.close();
          }
          catch (Exception e) {
              e.printStackTrace();
              System.exit(1);
          }
      }
  
      private void solve() throws Exception {
          int n = nextInt();
          pw.print(n + n / 2);
      }
  
      private BufferedReader br;
      private PrintWriter pw;
      private StringTokenizer tok;
  
      private String next() throws Exception {
          while (tok == null || !tok.hasMoreElements()) tok = new StringTokenizer(br.readLine());
          return tok.nextToken();
      }
  
      private int nextInt() throws Exception {
          return Integer.parseInt(next());
      }
  
  
  
  }