import java.util.Scanner;
public class Main{
  // TODO 自動生成されたメソッド・スタブ
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int i = scan.nextInt();
    String s = String.valueOf(i);
    String[] ss = s.split("");
    int count = 0;
    for(String masu : ss){
      if(masu.equals("1")) {
        count = count + 1;
      }
    }
    System.out.println(count);
    }
}
/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