source_code: //package Codeforces72;
  
  import java.util.Scanner;
  
  public class A {
  
  	/**
  	 * @param args
  	 */
  	public static void main(String[] args) {
  		Scanner in = new Scanner(System.in);
  		int n = in.nextInt();		
  		System.out.println((int)(n+n/2));
  	}
  
  }
  