import java.util.Scanner;

class Main{
    public static void main(String args[]){
        Scanner sc=new Scanner(System.in);
        String str=sc.nextLine();
        int cnt=0;
        for(int i=0;i<str.length();i++){
            if(str.charAt(i)=='1'){
                cnt++;
            }
        }
        System.out.print(cnt+"\n");
    }
}
/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