import java.util.*;

class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int cnt = 0;
        while(num != 0){
            if(num%10 == 1){cnt++ ;}
            num = num/10;
        }
        System.out.println(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