#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define numa(x,a) for(auto x: a)
#define ite iterator
#define mp make_pair
#define mt make_tuple
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL( c ) (c).begin(), (c).end()
#define gcd(a,b) __gcd(a,b)
#define mem(x,n) memset(x,n,sizeof(x))
#define endl "\n"
using namespace std;
template <int POS, class TUPLE> void deploy(std::ostream &os, const TUPLE &tuple){}
template <int POS, class TUPLE, class H, class ...Ts> void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get<POS>(t); deploy<POS + 1, TUPLE, Ts...>(os, t); }
template <class T> std::ostream& operator<<(std::ostream &os, std::vector<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::set<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T, class K> std::ostream& operator<<(std::ostream &os, std::map<T, K> &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; }
#define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); }
#define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); }
#define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); }
using ll = long long;
#define MAX_N 200100
int K,N;
vector <ll> interval_Eratosthenes(ll a,ll b){
  vector <bool> is_prime(MAX_N);
  vector <bool> is_prime_small(MAX_N);
  for(ll i = 0; (ll) i * i < b ; i++){
    is_prime_small[i] = true;
  }
  
  for(ll i = 0; i < b - a; i++){
    is_prime[i] = true;
  }
  for(ll i = 2 ; (ll) i * i < b; i++){
    if(is_prime_small[i]){
      for(ll j = 2 * i; (ll) j * j < b ; j+= i){
	is_prime_small[j] = false;
      }
      for(ll j = max(2LL,(a+i-1)/i) * i; j < b; j+= i){
	is_prime[j-a] = false;
      }
    }
  }

  vector <ll> ans;
  for(ll i = 0; i < b-a ; i++){
    if(is_prime[i]){
      ans.pb(a + i);
    }
  }
  return ans;
}
int calc(ll x){
  if(x < 10){
    return x;
  }
  ll ret = 0;
  while(x != 0){
    ret += x % 10;
    x /= 10;
  }
  return calc(ret);
}

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cin >> K >> N;
  auto pr = interval_Eratosthenes(max(2,K),N+1);
  auto pr2 = pr;
  rep(i,sz(pr)){
    pr[i] = calc(pr[i]);
  }
  //DEBUG1(pr);
  //DEBUG1(pr2);
  int ans = 0;
  int ans_num = 0;
  int memo[10];
  int start = 0;
  mem(memo,-1);
  rep(i,sz(pr)){
    if(memo[pr[i]] == -1){
      memo[pr[i]] = i;
    }else{
      if(ans < i-start){
        ans = i-start;
        ans_num = pr2[start];
      }else if(ans == i-start && ans_num <= pr2[start]){
        ans_num = pr2[start];
      }
      start = memo[pr[i]]+1;
      memo[pr[i]] = i;
      for(int j = 0; j <= 9;j++){
        if(memo[j] < start){
          memo[j] = -1;
        }
      }
    }
    //DEBUG3(i,start,ans_num);
  }
  if(ans < sz(pr)-start){
    ans = sz(pr)-start;
    ans_num = pr2[start];
  }else if(ans == sz(pr)-start && ans_num <= pr2[start]){
    //DEBUG2(start,ans_num);
    ans_num = pr2[start];
  }

  cout << ans_num << endl;
  return 0;
}