import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        int cnt = 0;
        for(int i=0; i<s.length(); i++){
            if(s.substring(i,i+1).equals("1")) cnt++;
        }
        
        scan.close();
        System.out.println(cnt);
    }
}
/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