#include<bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
const ll MOD=1000000007;
const ll INF=1000000010;
const ll LINF=4000000000000000010LL;
const int MAX=310;
const double EPS=1e-9;
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
vector<bool> eratosthenes(int n){
    vector<bool> prime(n,true);
    prime[0]=false;prime[1]=false;
    for(int i=2;i<=n;i++){
        if(prime[i]){
            for(int j=i*2;j<=n;j+=i){
                prime[j]=false;
            }
        }
    }
    return prime;
}
ll digitsum(ll n){
    ll sum=0;
    while(n>0){
        sum+=n%10;
        n/=10;
    }
	if(sum>10)return digitsum(sum);
    else return sum;
}

bool s[200010];
int main(){
	int k,n;cin>>k>>n;
	vector<bool> f=eratosthenes(n);
	vector<int> v,v2;
	for(int i=k;i<=n;i++){
		if(f[i]){
			v2.push_back(i);
			v.push_back(digitsum(i));
		}
	}
	int ma=1;
	int ans=v[0];
	int idx=0;
	s[v[0]]=true;
	for(int i=1;i<v.size();i++){
		if(s[v[i]]){
			for(;idx<i;idx++){
				s[v[idx]]=false;
				if(v[idx]==v[i]){
					idx++;
					break;
				}
			}
		}
		s[v[i]]=true;
		if(ma<=i-idx+1){
			ma=i-idx+1;
			ans=v2[idx];
		}
	}
	cout<<ans<<endl;
	return 0;
}