#include <iostream> 
#include <string> 
#include <vector> 
#include <cmath> 
#include <algorithm> 
#include <cstdlib> 
#include <ctime> 
#include <cstdio> 
#include <functional> 
#include <set> 
#include <sstream> 
#include <cctype>
#include <queue>

using namespace std; 

typedef pair<int,int> pii;
const int INF=(1<<30);


int f(long x){
	int sum=0;
	while(x){
		sum+=x%10;
		x/=10;
	}

	if(sum<10) return sum;
	else return f(sum);

}

vector<long> get_Prime(long K,long N){
	vector<bool> prime(N+1,true);
	prime[0]=prime[1]=false;

	for(long i=2;i*i<=N;i++){
		if(prime[i]){
			for(int j=2;i*j<=N;j++) prime[i*j]=false;
		}
	}

	vector<long> res;
	for(long i=K;i<=N;i++) if(prime[i]) res.push_back(i);

	return res;

}


int main(){

	long K,N;
	cin>>K>>N;

	vector<long> prime=get_Prime(K,N);

	//[K,N]に素数が存在しない場合は...？
	long len=1,res=prime[0];
	for(int i=0;i<prime.size();i++){
		set<long> s;
		for(int j=i;j<prime.size();j++){
			int h=f(prime[j]);
			if(s.find(h)!=s.end()) break;
			else s.insert(h);
		}

		if(len<=s.size()){
			len=s.size();
			res=prime[i];
		}

	}

	cout<<res<<endl;

	return 0;
}