Help!85!

#include <bits/stdc++.h>
using namespace std;
int change(string n, int b){
    int r = 0;
    for (char c : n){
        int d = c - '0';
        r = r * b + d;
    }
    return r;
}
int f(int p, int q, int r){
    for (int i = 2; i <= 16; i++){
        int n1 = change(to_string(p), i);
        int n2 = change(to_string(q), i);
        int ar = change(to_string(r), i);
        if (n1 * n2 == ar)
            return i;
    }
    return 0;
}
int main(){
    int p, q, r;
    cin >> p >> q >> r;
    cout << f(q, p, r);
    return 0;
}