#include <bits/stdc++.h>

#include <atcoder/all>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define FAST_IO                \
  ios::sync_with_stdio(false); \
  cin.tie(0);
const i64 INF = 1001001001001001001;
using Modint = atcoder::static_modint<998244353>;

vector<i64> getPrimes(int n) {
  vector<bool> isPrime(n + 1, true);
  isPrime[0] = isPrime[1] = false;
  for (int i = 2; i <= n; i ++) {
    if (isPrime[i]) {
      for (int j = i + i; j <= n; j += i) {
        isPrime[j] = false;
      }
    }
  }
  vector<i64> primes;
  for (int i = 3; i <= n; i ++) {
    if (isPrime[i]) {
      primes.push_back(i);
    }
  }
  return primes;
}


int main() {
  FAST_IO

  i64 L, R;
  cin >> L >> R;


  auto primes = getPrimes(10000);
  int m = primes.size();
  for (int i = 0; i < m; i ++) {
    auto a = primes[i];

    if (a * a * a * a >= R) break;
    for (int j = i + 1; j < m; j ++) {
      auto b = primes[j];
      if (a * a * b * b >= R) break;

      for (int k = j + 1; k < m; k ++) {
        auto c = primes[k];
        auto x = a * a * b * c;
        if(L <= x && x <= R) {
          cout << x << endl;
          return 0;
        }
      }
    }
  }
  cout << -1 << endl;
  return -1;
}