#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;
}

template<class T> T pow_mod(T A, T N, T M) {
    T res = 1 % M;
    A %= M;
    while (N) {
        if (N & 1) res = (res * A) % M;
        A = (A * A) % M;
        N >>= 1;
    }
    return res;
}

bool MillerRabin(long long N, vector<long long> A) {
    long long s = 0, d = N - 1;
    while (d % 2 == 0) {
        ++s;
        d >>= 1;
    }
    for (auto a : A) {
        if (N <= a) return true;
        long long t, x = pow_mod<__int128_t>(a, d, N);
        if (x != 1) {
            for (t = 0; t < s; ++t) {
                if (x == N - 1) break;
                x = __int128_t(x) * x % N;
            }
            if (t == s) return false;
        }
    }
    return true;
}

bool is_prime(long long N) {
    if (N <= 1) return false;
    if (N == 2) return true;
    if (N % 2 == 0) return false;
    if (N < 4759123141LL)
        return MillerRabin(N, {2, 7, 61});
    else
        return MillerRabin(N, {2, 325, 9375, 28178, 450775, 9780504, 1795265022});
}

int main() {
  FAST_IO

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



  auto primes = getPrimes(1000000);
  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;

      auto x = a * a * b;
      auto y = (L + x - 1) / x;
      if (y >= 1e6) {
        for (i64 c = y; x * c <= R; c ++) {
          if (is_prime(c)) {
            cout << x * c << endl;
            return 0;
          }
        }
      }

      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 0;
}