#include <bits/stdc++.h>
using namespace std;

#define M 200000
int dp[M + 1];
int isPrime[M + 1];

int main() {
	int k, n;
	cin >> k >> n;

	for (int i = 0;i < 10;i++) {
		dp[i] = i;
	}
	for (int i = 10;i <= M;i++) {
		int sum = 0;
		for (int j = i;j != 0;j /= 10) {
			sum += j % 10;
		}
		dp[i] = dp[sum];
	}

	vector<int> p;
	isPrime[0] = 0;
	isPrime[0] = 0;
	for (int i = 2;i <= M;i++) {
		isPrime[i] = -1;
	}
	for (int i = 2;i <= M;i++) {
		if (isPrime[i] == -1) {
			if (i >= k && i <= n) {
				p.push_back(i);
			}
			isPrime[i] = 1;
			for (int j = 2;i*j <= M;j++) {
				isPrime[i*j] = 0;
			}
		}
	}

	int ma = 0,ans;
	for (int i = 0;i < p.size();i++) {
		vector<int> is(10, false);
		int count = 0;
		for (int j = i;j < p.size();j++) {
			if (is[dp[p[j]]]) {
				break;
			}
			else {
				count++;
				is[dp[p[j]]] = true;
			}
		}
		if (ma <= count) {
			ma = count;
			ans = p[i];
		}
	}
	cout << ans << endl;

	return 0;
}