source_code: import java.io.IOException;
  import java.util.Scanner;
  
  
  public class A {
  	public static void main(String args[]) throws IOException {
  		Scanner sc = new Scanner(System.in);
  		int n = sc.nextInt();
  		System.out.println((2*n) - (n/2));
  		
  	}
  
  }
  