#include <iostream>
#include <queue>
#include <algorithm>
#include <vector>
#include <algorithm>
#include <set>
#include <cstring>
#include <cmath>
#include <map>
#include <fstream>
using namespace std;

int f(int x) {
    if(x == 0) {
        return 0;
    }
    return f(x / 10) + (x % 10);
}
int main() {

    cout << f(1234) << endl;

   return 0;
}
/*
 f(1234) --> f(123) + 4 = 6 + 4 = 10
 f(123) --> f(12) + 3 = 3 + 3 = 6
 f(12) --> f(1) + 2 = 1 + 2 = 3
 f(1) --> f(0) + 1 = 0 + 1 = 1
 f(0) = 0

 */