source_code: import java.io.PrintWriter;
  import java.util.Locale;
  import java.util.Scanner;
  
  public class A {
  	public static void main (String[] args){
  		Scanner in = new Scanner(System.in);
  		PrintWriter out = new PrintWriter(System.out);
  		
  		int n = in.nextInt();
  		
  		out.printf(Locale.US, "%d", n/2*3);
  		
  		out.close();
  	}
  }
  