import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Stack;

public class sample {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();       
        System.out.println(n+n/2);
    }
}