import java.util.Scanner;

public class Main {

    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        String a = sc.next();

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        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