#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
#include <map>
#include <stack>
#include <functional>
#include <complex>
#include <cmath>
#include <ccomplex>
using namespace std;

vector<int> primes;

void sieve(int n) {
	bool isPrime[200010];
	for (int i = 0; i < 200010; i++)isPrime[i] = true;
	isPrime[0] = false;
	isPrime[1] = false;
	for (int i = 0; i <= n; i++) {
		if (isPrime[i] == true) {
			primes.push_back(i);
			for (int j = i * 2; j <= n; j += i) {
				isPrime[j] = false;
			}
		}
	}
}

int FrankHash(int n) {
	string s = to_string(n);
	while (s.length() > 1) {
		int tmp = 0;
		for (int i = 0; i < s.length(); i++) {
			tmp += s[i] - '0';
		}
		s = to_string(tmp);
	}
	return s[0] - '0';
}

int main() {
	int k, n;
	cin >> k >> n;
	sieve(n);
	vector<int> v;
	vector<int> hashed;
	for (int i = 0; i < primes.size(); i++){
		if (primes[i] >= k && primes[i] <= n)v.push_back(primes[i]);
	}

	for (int i = 0; i < v.size(); i++) {
		cerr << FrankHash(v[i]) << endl;
		hashed.push_back(FrankHash(v[i]));
	}

	map<int, bool> mp;
	for (int i = 1; i < 10; i++) {
		mp[i] = false;
	}

	int s = 0;
	int t = 0;
	int mx = 0;
	int mx_len = 0;
	mp[hashed[s]] = true;
	while (1) {
		while (t + 1 < v.size() && mp[hashed[t + 1]] == false) {
			t++;
			mp[hashed[t]] = true;
			cerr << v[s] << " " << v[t] << endl;
		}
		
		if (mx_len < t - s + 1) {
			mx_len = t - s + 1;
			mx = v[s];
		}
		else if (mx_len == t - s + 1) {
			mx = max(mx, v[s]);
		}

		mp[hashed[s]] = false;
		s++;
		if (v.size() - s < mx_len)break;
		
		cerr << v[s] << " " << v[t] << " " << mx << " " << mx_len << endl << endl;
	}
	cout << mx << endl;

}