#include <iostream>

using namespace std;

int rec(int number) {
    if(number == 0) {
        return 0;
    }
    int cifra = number % 10;
    return rec(number / 10) + cifra;
}
int main()
{
    int broj;
    cin >> broj;
    cout << rec(broj) << endl;
    return 0;
}
/*
 rec(4313) = rec(431) + 3 = 8 + 3 = 11
 rec(431) = rec(43) + 1 = 7 + 1 = 8
 rec(43) = rec(4) + 3 = 4 + 3 = 7
 rec(4) = rec(0) + 4 = 0 + 4 = 4
 rec(0) = 0

 **/