import java.util.Arrays;
import java.util.*;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
      String s = sc.next();
      int count =0;
      for(int i=0;i<6;i++){
        if(s.charAt(i)=='1'){
          count++;
        }
      }
      System.out.println(count);
    }
}
