import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		int a;
		int ans=0;
		Scanner scan = new Scanner(System.in);
		a = scan.nextInt();
		for(int i = 0; i < 3; ++i) {
			if(a%10 == 1) {
				ans++;
			}
			a /= 10;
		}
		System.out.println(ans);
	}
}

/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