import java.util.Scanner;

public class Main {

      public static void main(String args[]){
        Scanner scan = new Scanner(System.in);
        
        int num = scan.nextInt();
          String str = Integer.toString(num); 
          
          int count = 0;
        char[] c = str.toCharArray();
        for(char c1 : c) {
            if(c1 == '1') {
            	count++;
            }
        }
          System.out.println(count);
        }

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz