#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

#define MAX_PRIME 500000 
bool isprime[MAX_PRIME+1]; 
vector<int> primes; 
void init_prime(){
  fill(isprime, isprime+MAX_PRIME+1, true); 
  isprime[0] = isprime[1] = false; 
  for(int i = 2; i <= MAX_PRIME; i++) { 
    if (isprime[i]) { 
      primes.push_back(i); 
      for(int j = i*2; j <= MAX_PRIME; j += i) 
      isprime[j] = false; 
    } 
  } 
}

int myhash(int x){
  if(x<10) return x;
  int ret = 0;
  while(x>0){
    ret += x%10;
    x /= 10;
  }
  return myhash(ret);
}

int main(){
  
  int K, N;
  cin >> K;
  cin >> N;

  init_prime();
  vector<int> hv, prm;
  rep(i,primes.size()){
    if(K <= primes[i] && primes[i] <= N){
      prm.push_back(primes[i]);
      hv.push_back(myhash(primes[i]));
    }
  }
  
  vector<int> last(10, -1);

  int len = -1, ret = -1;
  rep(i,hv.size()){
    rep(j,10){
      last[j] = max(last[j], last[hv[i]]);
    }
    int maxlen = -1, p = -1;
    rep(j,10){
      if(i-last[j]>maxlen){
        maxlen = i-last[j];
        p = last[j];
      }
    }
    if(maxlen >= len){
      len = maxlen;
      ret = prm[p+1];
    }
    last[hv[i]] = i;
  }
  
  cout << ret << endl;
  
  return 0;
}