import java.util.*;
class Main 
{
	public static void main(String[]args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(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