import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	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