#include <iostream>
using namespace std;

int rec (int n) {
    if (n < 10) return n;
    return 100 * rec(n / 100) + 11 * (n % 10);
}

int main () {

    cout << rec(135) << endl; // prints 155
    cout << rec(19683) << endl; // prints 16633, but how?

return 0;
}