#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cctype>
#include <tuple>
#include <climits>
#include <bitset>
#include <cassert>
#include <random>

#ifdef _MSC_VER
#include <agents.h>
#endif

#define FOR(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define REV(v) v.rbegin(), v.rend()
#define MEMSET(v, s) memset(v, s, sizeof(v))
#define UNIQUE(v) (v).erase(unique(ALL(v)), (v).end())
#define MP make_pair
#define MT make_tuple

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

vector<int> prime;
vector<int> h;
int np[200010];

int geth(string s){
	if (s.size() == 1) return s[0] - '0';
	return geth(to_string(accumulate(ALL(s), 0) - '0'*s.size()));
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	int k, n;
	cin >> k >> n;

	FOR(i, 2, 200000){
		if (!np[i]){
			for (int j = i * 2; j < 200000; j += i) np[j] = 1;

			if (i < k || i > n) continue;
			prime.push_back(i);
			h.push_back(geth(to_string(i)));
		}
	}

	int cnt[100] = {};

	int l = 0, r = 0;
	int sz = prime.size();
	bool ok = true;
	P ans = MP(0, 0);
	while (1){
		while (r < sz && ok){
			ans = max(ans, MP(r - l, prime[l]));
			if (++cnt[h[r++]] > 1) ok = false;
		}
		if (ok && l < sz) ans = max(ans, MP(r - l, prime[l]));

		if (l == r) break;

		if (--cnt[h[l++]] == 1) ok = true;
		if (ok && l < sz) ans = max(ans, MP(r - l, prime[l]));
	}
	//cout << ans.first << endl;
	cout << ans.second << endl;


	return 0;
}