#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())



#define MAX_N 1000000
int prime[MAX_N];//i番目の素数
bool is_prime[MAX_N+1];
int sieve(int K,int N){
	int p=0;
	memset(is_prime,true,sizeof(is_prime));
	is_prime[0]=is_prime[1]=false;
	for(int i=2;i<=N;i++){
		if(is_prime[i]){
			if(K<=i)prime[p++]=i;
			for(int j=2*i;j<=N;j+=i)is_prime[j]=false;
		}
	}
	return p;
}

int gomihash(int n){
	while(10<=n){
		int s=0;
		while(n){s+=n%10;n/=10;}
		n=s;
	}
	return n;
}

int main(){
	int K,N,m;
	cin>>K>>N;
	m=sieve(K,N);
	int cnt[10]={},ans=-1,maxlen=0,len=0;
	rep(i,m){
		int h=gomihash(prime[i]);
		len++;
		cnt[h]++;
		while(cnt[h]>=2)cnt[gomihash(prime[i-(--len)])]--;
		if(maxlen<=len){
			maxlen=len;
			ans=prime[i-len+1];
		}
	}
	cout<<ans<<endl;
	return 0;
}