#include"bits/stdc++.h"
using namespace std;
typedef long long ll;

vector<ll> primeEnumeration(ll n,ll k){
    vector<ll>res;
    vector<bool>isprime(n+1,true);

    for(ll i=2;i<=n;i++){
        if(isprime[i]){
            for(ll j=i*2;j<=n;j+=i){
                isprime[j]=false;
            }
            if(i>=k)res.push_back(i);
        }
    }
    return res;
}

template <class T> void chmax(T &a,T b){
    if(a<b)a=b;
}

ll hAsh(string x){
    ll res=0;
    for(ll i=0;i<x.size();i++){
        res+=x[i]-'0';
    }

    if(res<10)return res;

    return hAsh(to_string(res));
}

int main(){
    ll n,k;
    cin>>k>>n;

    vector<ll>prime;
    map<ll,ll>map;

    prime=primeEnumeration(n,k);

    ll ans=0;
    ll ans2=0;
    ll max=-1;

    for(ll i=0;i<prime.size();i++){
        ll hash=hAsh(to_string(prime[i]));
        if(map.count(hash)){
            if(max>map[hash]){
                if(ans<=i-max){
                    chmax(ans,i-max);
                    chmax(ans2,prime[max+1]);
                }
                map[hash]=i;
                continue;
            }

            if(ans<=i-map[hash]){
                chmax(ans,i-map[hash]);
                chmax(ans2,prime[map[hash]+1]);
            }

            max=map[hash];
            map[hash]=i;
        }else{
            if(ans<=i-max){
                chmax(ans,i-max);
                chmax(ans2,prime[max+1]);
            }
            map[hash]=i;
        }
    }
    cout<<ans2<<endl;
}