import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;

public class Main {

    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    private static final PrintWriter sysout = new PrintWriter(System.out, false);

    private static StringTokenizer buffer;

    private static String readLine() {
        buffer = null;
        try {
            return br.readLine();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static String read() {
        if (buffer == null || !buffer.hasMoreTokens()) {
            buffer = new StringTokenizer(readLine());
        }
        return buffer.nextToken();
    }

    private static int readInt() {
        return Integer.parseInt(read());
    }

    private static int[] readIntArray(int loop) {
        int[] result = new int[loop];
        for (int i = 0; i < loop; i++) {
            result[i] = readInt();
        }
        return result;
    }

    private static int[] splitInt() {
        String[] tmp = read().split("");
        int[] result = new int[tmp.length];
        for (int i = 0, n = tmp.length; i < n; i++) {
            result[i] = Integer.parseInt(tmp[i]);
        }
        return result;
    }

    private static long readLong() {
        return Long.parseLong(read());
    }

    private static double readDouble() {
        return Double.parseDouble(read());
    }

    public static void main(String[] args){
        run();
    }

    private static void run() {
        String[] input = readLine().split("");
        int count = 0;
        if (input[0].equals("1")) count++;
        if (input[1].equals("1")) count++;
        if (input[2].equals("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