#include <iostream>
#include <algorithm>
using namespace std;


int f(int number) {
    if(number == 0) {
        return 0;
    }

    int digit = number % 10;
    return digit + f(number / 10);
}
int main() {
    cout << f(1234) << endl;

    return 0;
}

// f(1234) = 4 + f(123) = 4 + 6 = 10
// f(123)  = 3 + f(12) = 3 + 3 = 6
// f(12)   = 2 + f(1) = 2 + 1 = 3
// f(1)    = 1 + f(0) = 1 + 0 = 1
// f(0)    = 0