#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <string>
#include <iomanip>
#include <map>
#include <set>
#include <cmath>
#include <cstdio>
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define FOR(i,m,n) for(int (i)=(m);(i)<(n);(i)++)
#define All(v) (v).begin(),(v).end()
typedef long long ll;

vector<bool> sieve(int x){//range...[0,x]
    vector<bool> flags(x+1,true);
    flags[0]=false,flags[1]=false;
    for(int i=2;i*i<=x;i++){
        if(!flags[i])continue;
        for(int mult = i*i;mult<x;mult+=i)
            flags[mult]=false;
    }
    return flags;
}

int frank_hash(int num){
    if(num/10==0)return num;
    else{
        int ret = 0;
        while(num>0){
            ret+=num%10;
            num/=10;
        }
        return frank_hash(ret);
    }
}

int main(){
    int K,N;
    cin >> K >> N;
    auto s = sieve(200000);
    vector<int> primes;
    for(int i=K;i<=N;i++){
        if(s[i])primes.push_back(i);
    }
    int m = primes.size();
    vector<int> hashed(m);
    rep(i,m){
        hashed[i]=frank_hash(primes[i]);
    }

    int left = 0,right=0;
    map<int,int> nums;
    int len = 0,res = 0;
    for(;right<m;){
        if(nums[hashed[right]]==0){
            nums[hashed[right]]++;
            right++;
        }else if(nums[hashed[left]]!=0){
            nums[hashed[left]]--;
            left++;
        }
        if(right-left>=len){
            len = right-left;
            res = primes[left];
        }
    }

    //rep(i,m)cout << hashed[i] << endl;
    cout << res << endl;

    return 0;
}