source_code: import java.io.*;
  import java.util.*;
  
  public class Main {
  
      public void solve() throws IOException {
          int n = nextInt();
          output.println(n / 2 * 3);
      }
  
      public void run() throws IOException {
          input = new BufferedReader(new InputStreamReader(System.in));
          output = new PrintWriter(System.out);
          solve();
          input.close();
          output.close();
      }
  
      BufferedReader input;
      PrintWriter output;
      StringTokenizer tok;
  
      String nextToken() throws IOException {
          while(tok == null || !tok.hasMoreTokens())
              tok = new StringTokenizer(input.readLine());
  
          return tok.nextToken();
      }
  
      int nextInt() throws IOException {
          return Integer.valueOf(nextToken());
      }
  
      long nextLong() throws IOException {
          return Long.valueOf(nextToken());
      }
  
      double nextDouble() throws IOException {
          return Double.valueOf(nextToken());
      }
  
      public static void main(String[] args) throws IOException {
          new Main().run();
      }
  }
  