import java.util.Scanner;

public class Main
{
    // https://atcoder.jp/contests/abc081/tasks/abc081_a
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        String input = sc.next();
        int answer = 0;
        for (char c : input.toCharArray()) {
            answer += c == '1' ? 1 : 0;
        }
        System.out.println(answer);
    }
}

/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