import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner S = new Scanner(System.in);
        int N = S.nextInt();
        int op = 0;

        while (N > 0) {
            if (N % 3 == 0) {
                N -= 3;
            } else {
                N -= 2;
            }
            op++;
        }
        System.out.println(op);
    }
}