import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String wk = sc.next();
    String[] ballArray = wk.split("");
    int ballNum = 0;
    for (int i = 0;i < ballArray.length;i++){
      if (ballArray[i].equals("1")) {
        ballNum = ballNum + 1;
      }
    }
	System.out.println(ballNum);
  }
}
/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