#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

map<int,int> factorize(int x){
  map<int,int> ret;
  int d, q;
  while(x>=4 && x%2==0){ret[2]++; x/=2;}
  d = 3; q = x/d;
  while(q>=d){
    if(x%d==0){ ret[d]++; x=q; }else{ d+=2; }
    q=x/d;
  }
  ret[x]++;
  return ret;
}
vector<int> divisor(int n){
  vector<int> ret;
  for(int i=1; i*i<=n; i++){
    if(n%i==0){
      ret.push_back(i);
      if(i!=n/i) ret.push_back(n/i);
    }
  }
  //sort(ret.begin(), ret.end());
  return ret;
}


int main(){
  int N, K;
  cin >> N >> K;

  map<int,int> f = factorize(N);

  int cnt = 0;
  int M = -1;
  
  REP(i,1,N){
    map<int,int> g = factorize(i);
    vector<int> d = divisor(i);

    int cmn = 0;
    FOR(it,g){
      cmn += min(f[it->first], it->second);
    }

    if(cmn >= K && d.size() > cnt){
      cnt = d.size();
      M = i;
    }
  }

  cout << M << endl;
  
  return 0;
}