source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.*;
  
  public class A {
  	public static void main(String[] args) throws IOException {
  		// TODO Auto-generated method stub
  		BufferedReader r=new BufferedReader(new InputStreamReader(System.in));
  		String s=r.readLine();
  		
  		int n=Integer.parseInt(s);
  		System.out.println(n*3/2);
  	}
  }
  