source_code: import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.util.Scanner;
  import java.util.StringTokenizer;
  
  public class CF {
  	public static void main(String[] args) throws IOException {
  		Scanner sc=new Scanner(System.in);
  		PrintWriter pw = new PrintWriter(System.out);
           int n=sc.nextInt();
           pw.print(n+n/2);
  	pw.close();
  	sc.close();
  }
  }