#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>

using namespace std;

#define REP(i,n)	for(int i=0;i<(n);++i)
#define REPS(i,s,t)	for(int i=(s);i<(t);++i)
#define PER(i,n)	for(int i=0;i>(n);--i)
#define PERS(i,s,t)	for(int i=(s);i>(t);--i)

#define INF 		2000000007
#define MINF		-200000007
#define MOD			17 	
// 2^20

#define MAX 		200005

typedef unsigned int 			uint;
typedef unsigned long long int	ull;
typedef long long int 			ll;

int dp[MAX];
bool is_prime[MAX];

void segment_sieve(int b){
	for(int i=2;i<b;++i)is_prime[i]=true;

	for(int i=2;(ll)i*i < b;++i){
		if(is_prime[i]){
			for(ll j=2LL*i;j<b;j+=i) is_prime[j] = false;
		}
	}
}

int add(int a){
	int suml = 0;
	if(a/10==0)return a;
	while(a){
		suml += a%10;
		a /=10;
	}
	return add(suml);
}

int main(){
	int K;cin>>K;
	int N;cin>>N;

	segment_sieve(N+1);
	vector<int> prime;
	REPS(i,K,N+1) if(is_prime[i])prime.push_back(i);

	vector<int> prime2(prime.size());
	REP(i,prime.size())prime2[i] = add(prime[i]);

	bool flag[10];REP(i,10)flag[i]=0;
	int cnt = 1;
	flag[prime2[0]]=1;
	for(int i=0,j=1;i<prime.size();++i){
		while(j<prime.size()){
			//cout << "  " << i << " " << j << endl;
			if(flag[prime2[j]]){
				dp[i]=cnt--;
				flag[prime2[i]]=0;
				break;
			}
			flag[prime2[j]]=1;
			j++;
			cnt++;
		}
		if(j==prime.size())dp[i]=cnt--;
	}
	int maxl=0;
	int point=0;
	REP(i,prime.size())
		if (dp[i] >= maxl){
			maxl = dp[i];
			point = i;
		}
	cout << prime[point] << endl;

	return 0;
}