import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int ans = n;
        while (n > 2) {
            // System.out.println(n);
            ans += n / 3;
            n = n / 3 + n % 3;
        }

        System.out.println(ans);
    }
}