// template version 1.7

// varibable settings {{{
using namespace std;
#include <iostream>
#include <bits/stdc++.h>

#define int long long
#define INF 1e18
// #define INF 2147483647
#define MOD 1e9+7
#define infile "../test/sample-1.in"
int dx[]={1, -1, 0, 0};
int dy[]={0, 0, 1, -1};
#define fi first
#define se second

// }}}

// define basic macro {{{
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)(b-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
template<class T> inline void chmax(T &a, const T &b) { if(a < b) a = b; }
template<class T> inline void chmin(T &a, const T &b) { if(a > b) a = b; }

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;
template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;

// dump macro
#ifdef PCM
  #include "dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;
// }}}

int n;
int k;

map<int, int> prime_factor(int n) { // 素因数分解 (o(√N)){{{
    map<int, int> res;
    for(int i = 2; i * i <= n; i++) {
        while(n % i == 0) {
            ++res[i];
            n /= i;
        }
    }
    if (n != 1) res[n] += 1;
    return res;
}
/*}}}*/

int check(auto a, auto b){
  int t=0;
  for(auto& el:a){
    t += min(a[el.first], b[el.first]);
  }
  if (t>=k) return true;
  else return false;
}

int solve(){
  cin>>n>>k;
  auto d = prime_factor(n);
  // dump(d);

  map<int, int> dp[n];
  dp[2][2]=1;
  int dc = 0;
  int M = -1;
  rep(i, 3, n){
    for (int j=2; j*j <= i; ++j){
      if (i%j==0){
        dp[i] = map<int, int>(dp[i/j]);
        dp[i][j]++;
        break;
      }
    }
    if (dp[i].empty()) dp[i][i]=1;
    // dump(i, dp[i]);
    if (check(d, dp[i])){
      int t=1;
      for (auto& el:dp[i]){
        t *= (el.second+1);
      }
      if (t>dc) {
        dc = t;
        M = i;
      }
    }
  }
  cout << M << endl;

  return 0;
}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
  solve();
  return 0;
} //}}}