#include <iostream>
#include <vector>
using namespace std;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))
#define FOR(i, f, t)        for(int(i)=(f);(i)<(t);(++i))

const int MAXN = 200000;

bool isprime[MAXN+1];
void primetable(int N){
    if(N>=2)isprime[2]=true;
    for(int i=3;i<=N;i+=2)isprime[i]=true;
    for(int i=3;i<=N;i+=2)if(isprime[i])for(int j=i+i;j<=N;j+=i)isprime[j]=false;
}

int fhash(int n){
    while(n > 9) n = n / 10 + n % 10; return n;
}

int main(){
    int K, N;
    cin >> K >> N;
    if(K < 1 || K > N || N < 1 || N > MAXN){ cerr << "err" << endl; };
    primetable(N);

    vector<int> p,q;
    FOR(i,K,N+1){
        if(!isprime[i]) continue;
        p.push_back(i); q.push_back(fhash(i));
    }
    int k[10];
    REP(i,10) k[i] = -1;
    int s = p.size(), l = 0, maxl = 0, lp = 0;
    REP(i,s){
        int j = k[q[i]];
        if(j >= 0) l = max(l, j + 1);
        k[q[i]] = i;
        if(maxl <= i - l + 1){
            maxl = i - l + 1; lp = p[l];
        }
    }
    cout << lp << endl;
    return 0;
}