import java.util.*;
public class Main {
	public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
}
        
        
/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