import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception{
		BufferedReader keyIn = new BufferedReader(new InputStreamReader(System.in));
		String s = keyIn.readLine();
		String[] array = s.split("");
		int count = 0;
		if(array[0].equals("1")) count++;
		if(array[1].equals("1")) count++;
		if(array[2].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