import java.util.Scanner;
class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(f(n));
    }
    public static int f(int n) {
        int count=n;
        while(n>=3) {
            n-=2;
            count++;
        }
        return count;
    }    
}