762A - k-th divisor - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;

int main()
{
	long long n,k,d;
	set<long long> a;
	cin>>n>>k;
	for(d=1;d*d<=n;d++)if(n%d==0)a.insert({d, n/d});
	if(k<=a.size())cout<<*next(a.begin(),k-1);else cout<<-1;
}