#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;

template <int m> ostream& operator<<(ostream& os, const static_modint<m>& a) {os << a.val(); return os;}
template <int m> ostream& operator<<(ostream& os, const dynamic_modint<m>& a) {os << a.val(); return os;}
template <int m> istream& operator>>(istream& is, static_modint<m>& a) {long long x; is >> x; a = x; return is;}
template <int m> istream& operator>>(istream& is, dynamic_modint<m>& a) {long long x; is >> x; a = x; return is;}
template<typename T> istream& operator>>(istream& is, vector<T>& v){int n = v.size(); assert(n > 0); rep(i, n) is >> v[i]; return is;}
template<typename U, typename T> ostream& operator<<(ostream& os, const pair<U, T>& p){os << p.first << ' ' << p.second; return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : " "); return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : ""); return os;}
template<typename T> ostream& operator<<(ostream& os, const set<T>& se){for(T x : se) os << x << " "; os << "\n"; return os;}
template<typename T> ostream& operator<<(ostream& os, const unordered_set<T>& se){for(T x : se) os << x << " "; os << "\n"; return os;}
template<typename S, auto op, auto e> ostream& operator<<(ostream& os, const atcoder::segtree<S, op, e>& seg){int n = seg.max_right(0, [](S){return true;}); rep(i, n) os << seg.get(i) << (i == n - 1 ? "\n" : " "); return os;}
template<typename S, auto op, auto e, typename F, auto mapping, auto composition, auto id> ostream& operator<<(ostream& os, const atcoder::lazy_segtree<S, op, e, F, mapping, composition, id>& seg){int n = seg.max_right(0, [](S){return true;}); rep(i, n) os << seg.get(i) << (i == n - 1 ? "\n" : " "); return os;}

template<typename T> void chmin(T& a, T b){a = min(a, b);}
template<typename T> void chmax(T& a, T b){a = max(a, b);}

const int M = 22500000;

int main(){
	vector<int> num(M + 1);
	vector<int> prime(M + 1);
	for(int x = 1; x <= M; x++) num[x] = x;
	for(int x = 2; x <= M; x++){
		if(num[x] != 1){
			prime[x] = 1;
			for(int y = 2 * x; y <= M; y += x){
				while(num[y] % x == 0){
					num[y] /= x;
				}
			}
		}
	}
	
	long long l, r;
	cin >> l >> r;
	vector<long long> f(r - l + 1);
	for(long long x = l; x <= r; x++) f[x - l] = x;
	
	if(r - l >= 45000) r = l + 45000;
	
	vector<vector<long long>> g(r - l + 1); 
	
	for(int x = 2; x <= M; x++){
		if(prime[x]){
			long long start = (l + (x - 1)) / x * x;
			long long end = r / x * x;
			for(long long y = start; y <= end; y += x){
				while(f[y - l] % x == 0){
					f[y - l] /= x;
					g[y - l].push_back(x);
				}	
			}
		}
	}
	for(long long x = l; x <= r; x++) if(f[x - l] != 1) g[x- l].push_back(f[x - l]);
	
	for(long long x = l; x <= r; x++){
		if(g[x - l].size() == 4 and g[x - l][0] != 2 and g[x - l][0] == g[x - l][1] and g[x - l][1] != g[x - l][2] and g[x - l][2] != g[x - l][3]){
			cout << x << "\n";
			return 0;
		}
	}
	cout << "-1\n";
	return 0;
}