#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <math.h>
#include <map>
using namespace std;
int hh(int x){
        if(x<10)return x;
        ostringstream to_str;
        to_str << x;
        string str=to_str.str();
        int sum=0;
        for(int i=0 ; i<str.size() ; i++ ){
                string tmp="";tmp+=str[i];
                istringstream to_int(tmp);
                int x;
                to_int>>x;
                sum+=x;
        }
        return hh(sum);
}
struct Info{
        bool sign;
        int locate;
};
int main(){
        int N,K;
        cin >> N >> K;
        vector <int> prime;
        vector <int> sss;
        for(int i=N ; i<=K ; i++ ){
                bool sign=true;
                for(int l=2 ; l<=sqrt(i) ; l++ ){
                        if(i%l==0){
                                sign=false;
                                break;
                        }
                }
                if(!sign || i==1 )continue;
                prime.push_back(hh(i));
                sss.push_back(i);
        }
        vector<int>::iterator itr;
        map<int,Info> used;
        int current,counter=0,max=0;
        int start;bool sign=true;
        for(int i=0 ; i<prime.size() ; i++ ){
                if(used[prime[i]].sign){
                        if(max<=counter){
                                max=counter;
                                current=start;
                        }
                        used[prime[i]].sign=false;
                        for(int j=0 ; j<i ; j++ )
                                used[prime[j]].sign=false;
                        i=used[prime[i]].locate+1;
                        sign=true;
                        counter=0;
                }if(sign){
                        start=i;
                        sign=false;
                }
                used[prime[i]].sign=true;
                used[prime[i]].locate=i;
                counter++;
        }if(max<=counter)
                current=start;
        cout << sss[current]<<endl;
}