import java.io.*;
import java.util.*;

import static java.lang.Math.min;

public class Main {

    void solve() throws IOException {
        int n = readInt();
        int mi = (int) 1e9;
        for (int a = 1; a < n; a++) {
            int b = n - a;
            int s = sum(a) + sum(b);
            if (s < mi) {
                mi = s;
            }
        }
        System.out.println(mi);
    }

    private int sum(int a) {
        String s = Integer.toString(a);
        int r = 0;
        for (int i = 0; i < s.length(); i++) {
            r += s.charAt(i) - '0';
        }
        return r;
    }

    //-------------------------------------------------

    final boolean ONLINE_JUDGE = !new File("input.txt").exists();

    BufferedReader in;
    PrintWriter out;
    StringTokenizer tok;

    public void run() {
        Runnable run = () -> {
            try {
                long startTime = System.currentTimeMillis();
                Locale.setDefault(Locale.US);
                if (ONLINE_JUDGE) {
                    in = new BufferedReader(new InputStreamReader(System.in));
                    out = new PrintWriter(System.out);
                } else {
                    in = new BufferedReader(new FileReader("input.txt"));
                    out = new PrintWriter("output.txt");
                }
                tok = new StringTokenizer("");
                solve();
                in.close();
                out.close();
                long endTime = System.currentTimeMillis();
                long totalMemory = Runtime.getRuntime().totalMemory();
                long freeMemory = Runtime.getRuntime().freeMemory();
                System.err.println();
                System.err.println("Time = " + (endTime - startTime) + " ms");
                //System.err.println("Memory = " + ((totalMemory - freeMemory) / 1024) + " KB");
            } catch (Throwable e) {
                e.printStackTrace(System.err);
                System.exit(-1);
            }
        };
        new Thread(null, run, "run", 256 * 1024 * 1024).start();
    }

    String readString() {
        while (!tok.hasMoreTokens()) {
            String line;
            try {
                line = in.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            if (line == null) return null;
            tok = new StringTokenizer(line);
        }
        return tok.nextToken();
    }

    int readInt() {
        return Integer.parseInt(readString());
    }

    long readLong() throws IOException {
        return Long.parseLong(readString());
    }

    double readDouble() throws IOException {
        return Double.parseDouble(readString());
    }

    void debug(Object... o) {
        if (!ONLINE_JUDGE) {
            System.err.println(Arrays.deepToString(o));
        }
    }

    long binpow(int a, int n) {
        long r = 1;
        while (n > 0) {
            if ((n & 1) > 0) {
                r *= a;
            }
            a *= a;
            n /= 2;
        }
        return r;
    }

    static long gcd(long x, long y) {
        return y == 0 ? x : gcd(y, x % y);
    }

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

Measured memory_bytes: 34724