#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <iomanip>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cassert>
#include <complex>
#include <stdio.h>
#include <time.h>
#include <numeric>
#include <random>
#include <unordered_map>
#include <unordered_set>
#define all(a) a.begin(),a.end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define pb push_back
#define debug(x) cerr << #x << ':' << x << '\n'
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef complex<ld> com;
constexpr int inf = 1000000010;
constexpr ll INF = 1000000000000000010;
constexpr ld eps = 1e-12;
constexpr ld pi = 3.141592653589793238;
template<class T, class U> inline bool chmax(T &a, const U &b) { if (a < b) { a = b; return true; } return false; }
template<class T, class U> inline bool chmin(T &a, const U &b) { if (a > b) { a = b; return true; } return false; }

vector<bool> is_prime(200010, true);

void init() {
	is_prime[0] = is_prime[1] = false;
	for (int i = 2; i < 200010; i++) {
		if (is_prime[i]) {
			for (int j = 2 * i; j < 200010; j += i) {
				is_prime[j] = false;
			}
		}
	}
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(20);
	init();

	int k, n;
	cin >> k >> n;
	int len = 0; int ans = -1, st = -1;
	vector<bool> ap(9);
	deque<P> que;
	for (int i = k; i <= n; i++) {
		if (!is_prime[i]) continue;
		if (st == -1) st = i;
		int val = i % 9;
		if (ap[val]) {
			while (que.front().first != val) {
				P num = que.front(); ap[num.first] = false;
				que.pop_front();
			}
			que.pop_front();
			que.push_back({ val,i });
			st = que.front().second;
		}
		else que.push_back({ val,i });
		ap[val] = true;
		if (len == que.size() || chmax(len, que.size())) ans = st;
	}
	cout << ans << '\n';
}