import java.util.Scanner;
  
    public class Main {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            
            int d = sc.nextInt();
            if(d<=9){
                System.out.println(d);
            }else if(d>9 && d%2==0){
                System.out.println((d+10)/20);
            }else{
                System.out.println(((d+9)/2)%10);
            }
        }
    }