import java.util.Scanner;

class Main {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);

        int ans = 0;
        String s = sc.next();
        for (Character c : s.toCharArray()) {
            if (c.equals('1'))
                ans++;
        }

        System.out.println(ans);
        sc.close();
    }
}

/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