source_code: import java.io.*;
  import java.lang.reflect.Array;
  import java.util.*;
   
  public class Main {
   
  	private BufferedReader input;
  	private PrintWriter output;
  	private StringTokenizer stoken;
   
  	String fin = "input";
  	String fout = "output";
   
   
  	private void solve() {
  
  		long a = nextInt();
  		
  		long res = (a / 2) * 3;
  
  		output.print(res);
  		
  	}
   
   
   
  	Main() throws IOException {
  		//input = new BufferedReader(new FileReader(fin + ".txt"));
  		//output = new PrintWriter(new FileWriter(fout + ".txt"));
  		input = new BufferedReader(new InputStreamReader(System.in));
  		output = new PrintWriter(System.out);
   
   
  		solve();
   
  		input.close();
  		output.flush();
  		output.close();
  	}
   
   
  	int nextInt() {
  		return Integer.parseInt(nextToken());
  	}
   
  	long nextLong() {
  		return Long.parseLong(nextToken());
  	}
   
  	double nextFloat() {
  		return Float.parseFloat(nextToken());
  	}
   
  	double nextDouble() {
  		return Double.parseDouble(nextToken());
  	}
   
  	String nextToken() {
  		while ((stoken == null) || (!stoken.hasMoreTokens())) {
  			try {
  				String line = input.readLine();
  				stoken = new StringTokenizer(line);
  			} catch (IOException e) {
  				e.printStackTrace();
  			}
  		}
  		return stoken.nextToken();
  	}
   
   
   
  	public static void main(String[] args) throws IOException {
  		new Main();
  	}
   
  }
  
  
  class Tarif {
  	public int abPlata;
  	public int tMin;
  	public int price;
  	public long res;
  }