//package ro.stancalau;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Created by Sorin on 4/29/2017.
 */
public class prog {

    long[] predef = new long[1000000000];

    public static void main(final String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
//        for(int n = 1; n <= nn; n++) {
            long l = n;
            l = n + (n / 3L);
            if (n > 3) {
                long between = 0;
                for(int k = n + 1; k <= l; k++) {
                    if (k % 3 == 0) between++;
                }
                l = l + between;
            }
//        for(int i = 1; i <= n; i++) {
//            if (l == 0) l++;
//            else if (l % 3 == 0) l = l + 2;
//            else l++;
//           System.out.println(l + "-" + i);
//        }

          //  System.out.println(l + "-" + n + "   ");

        System.out.println(l * 3L);
    }
}