import java.util.*;
public class Main {
    public static void main(String[] args) {
        // System.out.println(new App().getGreeting());
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        for(int i = 0; i < s.length(); i++){
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        }
        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