import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		int count = 0;
		for(int i = 0;i < 3;i++) {
		    if(s[i] - '0' == 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