source_code: import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.io.StreamTokenizer;
  
  public class A {
      private static StreamTokenizer in;
      private static PrintWriter out;
      
      private static int nextInt() throws Exception{
          in.nextToken();
          return (int)in.nval;
      }
      
      private static String nextString() throws Exception{
          in.nextToken();
          return in.sval;
      }
      
      static{
          in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
          out = new PrintWriter(System.out);
      }
      
      public static void main(String[] args)throws Exception{
          int n = nextInt();
          
          out.println(n*3/2);
          
          out.flush();
      }
  }
  