import java.util.Scanner;
 
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String str = sc.nextLine();
    String[] strAry = str.split("");
    
    int count = 0;
    if(strAry[0].equals("1")) count++;
    if(strAry[1].equals("1")) count++;
    if(strAry[2].equals("1")) count++;    
    System.out.println(count);
    
    return;
  }
}
/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