#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const int MAX_PRIME = 200100;
bool isPrime[MAX_PRIME + 1];
vector<int> primes;

int main() {
	fill(&isPrime[0], &isPrime[MAX_PRIME] + 1, true);
	isPrime[0] = false;
	isPrime[1] = false;
	for (int i = 2; i <= MAX_PRIME; ++i) {
		if (isPrime[i]) {
			for (int k = i * 2; k <= MAX_PRIME; k += i) {
				isPrime[k] = false;
			}
		}
	}
	int k, n;
	cin >> k >> n;
	for (int i = k; i <= n; ++i) {
		if (isPrime[i]) {
			primes.push_back(i);
		}
	}
	vector<int> hashes;
	for (size_t i = 0; i < primes.size(); ++i) {
		int x = primes[i];
		int hash;
		do {
			hash = 0;
			for (; x > 0; x /= 10) {
				hash += x % 10;
			}
			x = hash;
		} while (hash >= 10);
		hashes.push_back(hash);
	}
	int positions[10];
	fill(&positions[0], &positions[9] + 1, -1);
	int maxLength = 0;
	int maxFirst = 0;
	int first = 0;
	for (size_t last = 0; last < hashes.size(); ++last) {
		int h = hashes[last];
		if (positions[h] >= first) {
			first = positions[h] + 1;
		}
		positions[h] = last;
		int length = last - first + 1;
		if (maxLength <= length) {
			maxLength = length;
			maxFirst = first;
		}
	}
	cout << primes[maxFirst] << endl;
	return 0;
}