import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
      //入力値を取り込む
      Scanner sc = new Scanner(System.in);
      //0を消去して1だけ残し、その長さを出力すれば1の個数になる
      //replaceよりもreplaceAllの方が早い、なぜ？
      int i = sc.next().replaceAll("0","").length();
      //出力する
      System.out.println(i);
    }
}


/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