#include <iostream>
#include <string>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <iomanip>

using namespace std;

#define REP(i, n) for(ll i = 0;i < n;i++)
#define REPR(i, n) for(ll i = n;i >= 0;i--)
#define FOR(i, m, n) for(ll i = m;i < n;i++)
#define FORR(i, m, n) for(ll i = m;i >= n;i--)
#define REPO(i, n) for(ll i = 1;i <= n;i++)
#define ll long long
#define INF (ll)1 << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(),n.end()
#define MOD 1000000007
#define P pair<ll, ll>


ll a, b, ma = 0, ans;

vector<ll> prime, h;

bool IsPrime(ll n) {
	if (n <= 1)return false;
	for (ll i = 2; i <= sqrt(n); i++)
	{
		if (n % i == 0)return false;
	}
	return true;
}

int hs(ll a) {
	ll res = a;
	while (res > 9) {
		ll next = 0;
		while (res > 0) {
			next += res % 10;
			res /= 10;
		}
		res = next;
	}
	return res;
}

int main() {
	cin >> a >> b;
	FOR(i, a, b + 1)if (IsPrime(i))prime.push_back(i);
	REP(i, prime.size())h.push_back(hs(prime[i]));
	REPR(i, h.size() - 1) {
		ll now = 0;
		set<ll> se;
		FOR(j, i, h.size()) {
			if (se.find(h[j]) != se.end())break;
			else {
				se.insert(h[j]);
				now++;
			}
		}
		if (ma < now) {
			ma = now;
			ans = prime[i];
		}
	}
	
	
	cout << ans << endl;
}