import java.util.scanner;
public class Main {
    public static void main(string[] args) {
        Scanner scanner = new Scanner(system.in);
        int n = scanner.nexInt();
        scanner.close();
        
        if (n<0) {
            system.out.println("Invalid input");
        } else {
            system.out.println(sumofDigits(n));
        }
    }
    
    public static int sumofDigits(int number) {
        int sum = 0;
        int tempNumber = Math.abs(number);
        
        while (tempNumber > 0) {
            int digit = tempNumber % 10;
            sum += digit;
            tempNumber /= 10;
        }
        return sum;
    }
}