#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
const ll dx[9]={0,1,0,-1,1,-1,1,-1,0};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}


struct osak{
    vector<long long> lpf;// least prime factor
    vector<long long> prime;// prime table
    osak(long long n){//linear_sieve
        lpf=vector<long long>(n+1,-1);
        for (int d = 2; d <= n; ++d) {
          if(lpf[d]==-1){
            lpf[d]=d;prime.emplace_back(d);
          }
          for(auto p:prime){
            if(p*d>n||p>lpf[d])break;
            lpf[p*d]=p;
          }
        }
    }
    map<long long,long long> factor(int n) {
        map<long long,long long> factor;
        while (n > 1) {
            factor[lpf[n]]++;
            n /= lpf[n];
        }
        return factor;
    }

    vector<long long> divisor(int N){//O(div.size())
        map<long long,long long> facs=factor(N);
        vector<long long> ret={1};
        for(auto p:facs){
            ll range=ret.size();
            ll now=1;
            for(int i=0;i<p.se;i++){
                now*=p.fi;
                for(int j=0;j<range;j++){
                    ret.emplace_back(ret[j]*now);
                }
            }
        }
        sort(ret.begin(),ret.end());
        return ret;
    }
};


int main(){
  ll n,k;cin >> n >> k;
  osak os(n+10);
  auto fs=os.factor(n);
  ll divs=0;ll ans=-1;
  for(ll i=2;i<n;i++){
    auto facs=os.factor(i);
    ll cnt=0;
    for(auto [p,vs]:fs){
      cnt+=min(vs,facs[p]);
    }
    //cout << cnt << endl;
    if(cnt<k)continue;
    if(chmax(divs,(ll)os.divisor(i).size()))ans=i;
  }
  cout << ans << endl;
}