import java.util.*;
public class Main {
	public static void main(String[] args){
		//データ取り込み
		Scanner sc = new Scanner(System.in);
		//String S = sc.next();
		//int N = sc.nextInt();
		//System.out.println();
		String S = sc.next();
		int cnt = 0;
		
		for(char a : S.toCharArray()){
			if(a == '1'){
				cnt++;
			}
		}
		System.out.println(cnt);
	}
}
/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