#include <iostream>
#include <bits/stdc++.h>
#define Kirlos ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define ll long long
#define pb(k) push_back(k)
#define fi first
#define se second
#define endl '\n'
#define mp(x,y) make_pair(x,y)
#define MOD 1000000007
#define all(x) x.begin(), x.end()
#define PI acos(-1)
#define sin(x) sin((x)*PI/180)
#define cos(x) cos((x)*PI/180)
#define tan(x) tan((x)*PI/180)
#define Ones(x) __builtin_popcountll(x)
using namespace std;
void solve()
{
ll n,k;
cin>>n>>k;
vector<ll>div;
for(int i=1; (ll)i*i<=n; i++)
{
if(n%i==0)
{
div.push_back(i);
if(n/i!=i)
{
div.push_back(n/i);
}
}
}
sort(all(div));
if(k>div.size())
{
cout<<-1;
}
else
{
cout<<div[k-1];
}
}
int main()
{
Kirlos
ll t;
t=1;
//cin>>t;
while(t--)
{
solve();
}
return 0;
}
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