source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.LinkedList;
  import java.util.Scanner;
  import java.util.Stack;
  
  public class sample {
      public static void main(String[] args) {
          Scanner in = new Scanner(System.in);
          int n = in.nextInt();       
          System.out.println(n+n/2);
      }
  }