#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

void findPrime(int N, vector<bool>& isPrime)
{
    isPrime.assign(N+1, true);
    isPrime[0] = isPrime[1] = false;
    for(int i=2; i*i<=N; i++){
        if(isPrime[i]){
            for(int j=i; i*j<=N; j++){
                isPrime[i*j] = false;
            }
        }
    }
}

int getHash(int a)
{
    while(a >= 10){
        int b = 0;
        while(a > 0){
            b += a % 10;
            a /= 10;
        }
        a = b;
    }
    return a;
}

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

    vector<bool> isPrime;
    findPrime(n, isPrime);
    vector<pair<int, int> > p;
    for(int i=k; i<=n; ++i){
        if(isPrime[i])
            p.push_back(make_pair(i, getHash(i)));
    }

    vector<int> cnt(10, 0);
    int ret = -1;
    int maxLen = 0;
    unsigned j = 0;
    for(unsigned i=0; i<p.size(); ++i){
        ++ cnt[p[i].second];
        while(cnt[p[i].second] > 1){
            -- cnt[p[j].second];
            ++ j;
        }
        int len = i - j + 1;
        if(len >= maxLen){
            maxLen = len;
            ret = p[j].first;
        }
    }
    cout << ret << endl;

    return 0;
}