#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

vector<int32_t> make_primes(int32_t a, int32_t b){
	vector<int32_t> ps;
	bool e[b + 1];
	fill(e, e + b + 1, true);
	for(int32_t i = 2; i <= b; i++) if(e[i]){
		if(a <= i) ps.emplace_back(i);
		for(int32_t j = 2 * i; j <= b; j += i) e[j] = false;
	}
	return ps;
}

int main(){
	int32_t a, b;
	cin >> a >> b;
	vector<int32_t> ps = make_primes(a, b), hashed = ps;
	for(auto& p:hashed) while(10 <= p) p = p / 10 + p % 10;
	int32_t ans, maxi = 0, lastp[10]{};
	for(int32_t i = 0, lpmax = 0; i < hashed.size(); i++){
		lpmax = max(lpmax, lastp[hashed[i]]);
		int32_t dist = i - lpmax + 1;
		if(maxi <= dist){
			maxi = dist;
			ans = ps[lpmax + 1];
		}
		lastp[hashed[i]] = i;
	}
	cout << ans << endl;
}