import java.util.*;

public class Main {
	public static void main(String[] args){
		//入力値を受け取る
		Scanner scanner = new Scanner(System.in);
		String input = scanner.nextLine();
		//inputのなかで"1"に一致する数をカウント
		int count = 0;
		for(char x: input.toCharArray()){
			if(x == '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