import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();   // four-digit number (1000–9999)

        int sum = 0;
        int temp = num;
        while (temp > 0) {
            sum += temp % 10;     // add last digit
            temp /= 10;           // remove last digit
        }

        System.out.println(sum);
    }
}