#include <bits/stdc++.h>
using namespace std;

#define rep(i,j,n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(), i.rend()
#define INF 1e9
#define LINF 1e18
const int mod = 1e9 + 7;

typedef long long i64;
typedef pair<int, int> pi;

template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;

i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcd(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};

int PrimeFactor(long long n) {
  int cnt = 0;
  for(long long i = 2; i * i <= n; ++i) {
    while(n % i == 0) {
      cnt++;
      n /= i;
    }
  }
  if(n != 1) cnt++;
  return cnt;
}

int FactorCount(long long n) {
  map<long long, int> res;
  for(long long i = 2; i * i <= n; ++i) {
    if(n % i == 0 && !res.count(i)) res[i] = 0;
    while(n % i == 0) {
      res[i]++;
      n /= i;
    }
  }
  if(n != 1) res[n] = 1;

  int fact = 1;
  for(auto &it : res) {
    fact *= (it.second + 1);
  }
  return fact;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, k;
  cin >> n >> k;

  int ans = -1, fact = 0;
  rep(i, 1, n) {
    if(FactorCount(i) > fact && PrimeFactor(gcd(n, i)) >= k) {
      ans = i;
      fact = FactorCount(i);
    }
  }
  cout << ans << endl;
}