#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
// using namespace atcoder;
// using mint = modint1000000007;
// const int mod = 1000000007;
// using mint = modint998244353;
// const int mod = 998244353;
// const int INF = 1e9;
// const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i, l, r) for (int i = (l); i < (r); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rrep2(i, l, r) for (int i = (r)-1; i >= (l); --i)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define P pair<int, int>
template<typename A, typename B> inline bool chmax(A &a, const B &b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A &a, const B &b) { if (a > b) { a = b; return true; } return false; }
std::vector<long long> sieveOfEratosthenes(long long  n = 23000000) {
	std::vector<bool>p(n + 1, true);
	std::vector<long long>ret;
	p[0] = false;
	p[1] = false;
	for (int i = 2; i <= n; ++i) {
		if (!p[i]) continue;
		ret.push_back(i);
		for (int j = 2 * i; j <= n; j += i) p[j] = false;
	}
	return ret;
}
//long long にしているのは p*pとかでこまらないように
int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	long long l, r; cin >> l >> r;
	r = min(l + 45000, r);
	int width = r - l + 1;
	vector div(width, vector<long long>());
	auto ps = sieveOfEratosthenes();

	vector<long long> now(r - l + 1);
	for (long long i = l; i <= r; i++) {
		now[i - l] = i;
	}
	for (auto p : ps) {
		if (p == 2)continue;
		long long mnv = ((l + p - 1) / p)*p;
		for (long long i = mnv; i < r; i += p) {
			while (now[i - l] % p == 0) {
				now[i - l] /= p;
				div[i - l].push_back(p);
			}
		}
	}
	for (long long i = l; i <= r; ++i) {
		if (now[i - l] != 1)div[i - l].push_back(now[i - l]);
	}
	for (int i = 0; i < width; ++i) {
		if (div[i].size() != 4)continue;
		if (div[i][0] != div[i][1])continue;
		if (div[i][1] >= div[i][2])continue;
		if (div[i][2] >= div[i][3])continue;
		cout << l + i << endl;
		return 0;
	}
	cout << -1 << endl;
	return 0;
}