#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

template<class Z> map<Z, int> factorize(Z n) {
  map<Z, int> res;
  for (Z i = 2; i * i <= n; ++i) while (n % i == 0) ++res[i], n /= i;
  if (n != 1) ++res[n];
  return res;
}
template<class Z> V<Z> divisor(Z n) {
  V<Z> res;
  Z i;
  for (i = 1; i * i < n; ++i) if (n % i == 0) res.push_back(i), res.push_back(n / i);
  if (i * i == n) res.push_back(i);
  sort(begin(res), end(res));
  return res;
}

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n, k; cin >> n >> k;
  int res = -1, mx = 0;
  for (int i = 1; i < n; ++i) {
    int g = __gcd(i, n);
    int s = 0;
    for (const auto& e : factorize(g)) s += e.second;
    if (s < k) continue;
    int sz = divisor(i).size();
    if (sz > mx) {
      mx = sz; 
      res = i;
    }
  }
  cout << res << '\n';
}