import java.util.Scanner;

public class Main{
    
    public static void main(String...args){
        Scanner scanner=new Scanner(System.in 

);
        while(scanner.hasNext()){
            int n=scanner.nextInt();
            int total=n/3*2;
            if(n%3!=0){
                total++;
            }
            System.out.println(total);
        }
    }
}