import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
	
		String s = sc.next();
	int number = 0;	
      // スペース区切りの整数の入力
		int flag = 0;
      for(int i=0;i<3;i++){
      if(s.charAt(i)=='1'){
        number++;
      }}
		// 出力
    
		System.out.println(number);
	
      }
}
/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