#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<ll,ll> ;
const ll INF = 1e18;
const int MOD = 1000000007;

map<ll,ll> getPrimes_(ll x){
        map<ll,ll> res;
        for(ll i = 2; i * i <= x;i++){
                if(x%i ==0){
                        res[i] = 0;
                        while(x%i ==0) x /= i,res[i]++;
                }
        }
        if( x > 1) res[x] = 1;
        return res;
}

ll cnt_div(map<ll,ll> p){
    ll res = 1;
    for(auto k:p){
        res *= k.second + 1;
    }
    return res;
}

int main(){
    ll n;
    int k;
    cin >> n >> k;
    ll cnt_max = 0;
    ll ans = -1;
    map<ll,ll> n_prime = getPrimes_(n);
    for(int i=1;i<n;i++){
        map<ll,ll> i_prime = getPrimes_(i);
        int res = 0;
        for(auto p:i_prime){
            res += min(p.second,n_prime[p.first]);
        }
        if(res >= k){
            ll cnt = cnt_div(i_prime);
            if(cnt_max < cnt ) ans = i,cnt_max = cnt;
        }
    }
    cout << ans << endl;
    return 0;
}