#include <iostream>
using namespace std;

int sumOfDigits(int &sum, int number)
{
    if (number / 10 == 0)
    {
        sum += number;
        return sum;
    }

    else
        sum += number % 10;

        sumOfDigits(sum, number / 10);
}


int main()
{
    int number;
    int sum = 0;
    cin >> number;
    cout << sumOfDigits(sum, number);


    return 0;
}