#include <iostream>
#include <vector>

using namespace std;

int K, N;
bool is_prime[200001];

int main() {
	cin >> K >> N;
	for (int i = 0; i <= 200000; i++) {
		is_prime[i] = true;
	}
	is_prime[0] = false;
	is_prime[1] = false;
	for (int d = 2; d * d <= 200000; d++) {
		if (is_prime[d]) {
			for (int dd = d + d; dd <= 200000; dd += d) {
				is_prime[dd] = false;
			}
		}
	}
	vector<int> primes;
	vector<int> hashes;
	for (int i = K; i <= N; i++) {
		if (is_prime[i]) {
			primes.push_back(i);
			int n = i;
			while (n >= 10) {
				int nn = n;
				n = 0;
				while (nn > 0) {
					n += nn % 10;
					nn /= 10;
				}
			}
			hashes.push_back(n);
		}
	}
	int cnt[10];
	for (int i = 0; i < 10; i++) {
		cnt[i] = 0;
	}
	int res = -1;
	int best = 0;
	int s = 0, t = 0;
	while (s < primes.size()) {
		while (t < primes.size() && cnt[hashes[t]] == 0) {
			cnt[hashes[t]]++;
			t++;
		}
		if (t - s >= best) {
			res = primes[s];
			best = t - s;
		}
		cnt[hashes[s]]--;
		s++;
	}
	cout << res << endl;
	return 0;
}