source_code: import java.io.*;
  import java.util.*;
  import java.math.*;
  
  public class A {
      private void solve() throws IOException {
          int n = nextInt();
          int r = n;
          n *= 2;
          n -= (0.5*r);
          System.out.println(n);
      }
  
      public static void main(String[] args) {
          new A().run();
      }
  
      BufferedReader reader;
      StringTokenizer tokenizer;
      PrintWriter writer;
  
      public void run() {
          try {
              reader = new BufferedReader(new InputStreamReader(System.in));
              tokenizer = null;
              writer = new PrintWriter(System.out);
              solve();
              reader.close();
              writer.close();
          } catch (Exception e) {
              e.printStackTrace();
              System.exit(1);
          }
      }
  
      int[] readIntArray(int size) throws IOException {
          int[] res = new int[size];
          for (int i = 0; i < size; i++) {
              res[i] = nextInt();
          }
          return res;
      }
  
      long[] readLongArray(int size) throws IOException {
          long[] res = new long[size];
          for (int i = 0; i < size; i++) {
              res[i] = nextLong();
          }
          return res;
      }
  
      double[] readDoubleArray(int size) throws IOException {
          double[] res = new double[size];
          for (int i = 0; i < size; i++) {
              res[i] = nextDouble();
          }
          return res;
      }
  
      int nextInt() throws IOException {
          return Integer.parseInt(nextToken());
      }
  
      long nextLong() throws IOException {
          return Long.parseLong(nextToken());
      }
  
      double nextDouble() throws IOException {
          return Double.parseDouble(nextToken());
      }
  
      BigInteger nextBigInteger() throws IOException {
          return new BigInteger(nextToken());
      }
  
      String nextToken() throws IOException {
          while (tokenizer == null || !tokenizer.hasMoreTokens()) {
              tokenizer = new StringTokenizer(reader.readLine());
          }
          return tokenizer.nextToken();
      }
  }
  