import java.util.*;

public class Main {
		public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String num = sc.nextLine();
		String[] numArray = num.split("");
		int count = 0;
		for(int i = 0;i<numArray.length;i++) {
			int[] numInt = new int[numArray.length];
			numInt[i] = Integer.parseInt(numArray[i]);

			if(numInt[i] == 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