source_code: import java.io.BufferedReader;
  import java.io.InputStreamReader;
  
  public class Govnokod {
  
  	public static void main(String args[]) {
  		try {
  			InputStreamReader isr = new InputStreamReader(System.in);
  			BufferedReader br = new BufferedReader(isr);
  
  			while (true) {
  				String str = br.readLine();
  				int i = Integer.parseInt(str);
  
  				System.out.println(i*2-i/2);
  
  				return;
  			}
  		} catch (Exception e) {
  			e.printStackTrace();
  		}
  	}
  
  }
  