func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     long long n, k;     cin >> n >> k;     set<long long> a = {1, n};     for (long long d = 2; d <= min((long long)sqrt(n) + 10, n - 1); d++) {       if (n % d == 0) {         a.insert(d);         a.insert(n / d);       }     }     long long ans = -1;     if (a.size() >= k) {       auto it = next(a.begin(), k - 1);       ans = *it;     }     cout << ans << endl;   }   