#define _CRT_SECURE_NO_WARNINGS
#include <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <cmath>
#include <ctype.h>
#include <ctime>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <cctype>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <numeric>
#include <complex>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <iostream>
#include <iterator>
#include <algorithm>
#define aLL(g) (g).begin(),(g).end()
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define F(i,j,k) fill(i[0],i[0]+j*j,k)
#define P(p) cout<<(p)<<endl;
#define EXISt(s,e) ((s).find(e)!=(s).end())
#define INF 1<<25
#define MAX 100000000
#define pb push_back
#define mp make_pair
using namespace std;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<double> vd;
typedef pair<int, int> pii;
typedef pair<long, long> pll;
typedef pair<pair<int, int>, int> pp;
typedef long long ll;
int dx[] = { 0, 1, 0, -1 };
int dy[] = { -1, 0, 1, 0 };

int sttoi(std::string str) {
	int ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

bool sort_greater(const pair<string, int> &a, const pair<string, int> &b) {
	return a.second > b.second;
}
int gcd(int a, int b){
	if (b > a)swap(a, b);if (b == 0)return a;else{return gcd(b, a%b);}
}

bool makePrime(int n){
	if (n == 1) return false;
	for (int i = 3; i*i <= n; i += 2){
		if (n%i == 0) return false;
	}
	return true;
}

int hash1(string s){
	int sum = 0;
	for (int j = 0; j < s.length(); j++){
		sum += s[j] - '0';
	}
	return sum;
}

void solve() {
	int n, m;
	cin >> n >> m;
	vector<int> prime;
	vector<int> hashed;
	for (int i = n; i <= m; i++){
		if (i % 2 != 0){
			if (makePrime(i)){
				prime.push_back(i);
			}
		}
	}
	for (int i = 0; i < prime.size(); i++){
		string num = to_string(prime[i]);
		int tmp = hash1(num);
		while (tmp >= 10){
			tmp = hash1(to_string(tmp));
		}
		hashed.push_back(tmp);
	}
	int left = 0, right = 0;
	int maxi = -1;
	int ans;
	int count[10];
	fill(count, count + 10, 0);
	while (right < hashed.size()){
		count[hashed[right]]++;
		while (count[hashed[right]] == 2){
			count[hashed[left++]]--;
		}
		if (maxi <= right - left + 1){
			ans = prime[left];
			maxi = right - left + 1;
		}
		right++;
	}
	P(ans);
}

int main() {
	solve();
	return 0;
}