#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int rec(int number) {
    if(number == 0) {
        return 0;
    }
    int digit = number % 10;
    return rec(number / 10) + digit;
}

int main() {
   
   cout <<  rec(1304) << endl;
    return 0;
}
// rec(1304) = rec(130) + 4 = 4 + 4 = 8
// rec(130) = rec(13) + 0 = 4 + 0 = 4
// rec(13)  = rec(1) + 3 = 1 + 3 = 4
// rec(1) = rec(0) + 1 = 0 + 1 = 1
// rec(0) = 0