import java.util.*;

public class Main{
	public static void main(String[] args){

    Scanner scanner = new Scanner(System.in);

    String x = scanner.nextLine();
    String[] str = x.split("");
    int a = 0;
    for(String s : str){
    	if(s.equals("1")){a ++ ;}
    }
    System.out.println(a);
    }
}
/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