source_code: 
  
  import java.io.IOException;
  import java.util.Locale;
  import java.util.Scanner;
  
  public class A {
  	
  	private void processInput() throws IOException {
  		Scanner in = new Scanner(System.in);
  		
  		int n = in.nextInt();
  		long res = go(n);
  
  		System.out.printf(Locale.ENGLISH, "%d\n", res);			
  
  	
  
  		
  		in.close();
  	}
  
  	private long go(long n) {
  		
  		long res = 3*n / 2;
  		
  
  		return res;
  	}
  	
  	public static void main(String[] args) throws Exception {
  		A a = new A();
  		a.processInput();
  	}
  }
  