import java.util.*;
public class Main{
    public static void main(String args[]){
        Scanner scanner = new Scanner(System.in);
        String x = scanner.nextLine();
        int r = 3;
        int s = 0;

        for(int i = 0;i < r;i++){
            if(x.charAt(i) == '1'){
                s++;
            }
        }
        System.out.println(s);
    }
}
/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