//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();
        long l = n;
        l = n +  n / 3L;
        if (n % 3 != 0) {
            l = l + 1L;
        }
//        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 * 3L);
    }
}