source_code: 
  import java.io.*;
  import java.util.*;
  import static java.lang.Math.*;
  
  public class BetaRound72_Div2_A implements Runnable {
  
  	final boolean ONLINE_JUDGE = System.getProperty("ONLINE_JUDGE") != null;
  	BufferedReader in;
  	PrintWriter out;
  	StringTokenizer tok = new StringTokenizer("");
  
  	void init() throws IOException {
  		if (ONLINE_JUDGE) {
  			in = new BufferedReader(new InputStreamReader(System.in));
  			out = new PrintWriter(System.out);
  		} else {
  			in = new BufferedReader(new FileReader("input.txt"));
  			out = new PrintWriter("output.txt");
  		}
  	}
  
  	String readString() throws IOException {
  		while (!tok.hasMoreTokens()) {
  			tok = new StringTokenizer(in.readLine());
  		}
  		return tok.nextToken();
  	}
  
  	int readInt() throws IOException {
  		return Integer.parseInt(readString());
  	}
  
  	@Override
  	public void run() {
  		try {
  			long t1 = System.currentTimeMillis();
  			init();
  			Locale.setDefault(Locale.US);
  			solve();
  			out.close();
  			long t2 = System.currentTimeMillis();
  			System.err.println("Time = " + (t2 - t1));
  		} catch (Exception e) {
  			e.printStackTrace(System.err);
  			System.exit(-1);
  		}
  	}
  
  	public static void main(String[] args) {
  		new Thread(new BetaRound72_Div2_A()).start();
  	}
  	
  	void solve() throws IOException {
  		int n = readInt();
  		int ans = n * 3 / 2;
  		out.print(ans);
  	}
  	
  }
  