// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
// functions
template <typename T> void unique(T& c){c.erase(std::unique(c.begin(), c.end()), c.end());}
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << "(" << p.first << ", " << p.second << ")"; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(20);}
} fast_io_;

template <typename T>
vector<T> list_prime(T n){
  vector<T> res;
  vector<bool> i_prime = vector<bool>(n+1, true);
  i_prime[0] = i_prime[1] = false;
  for(ll i = 2; i <= n; i++){
    if(i_prime[i]){
      res.push_back(i);
      for(ll j = 2; j * i <= n; j++){
        i_prime[i * j] = false;
      }
    }
  }
  return res;
}

int calc(int i){
  int res = 0;
  if(i < 10)return i;
  while(i){
    res += i % 10;
    i /= 10;
  }
  return calc(res);
}

int main(int argc, char const* argv[])
{
  int k, n; cin >> k >> n;
  auto p = list_prime(n);
  vector<int> cnt(10, -1);
  int len = 0, res = -1;
  deque<int> dq;
  rep(i, sz(p)){
    if(p[i] < k)continue;
    int h = calc(p[i]);
    if(cnt[h] == -1){
      cnt[h] = p[i];
    }else{
      /*
      cerr << p[i] << ": " << cnt << endl;
      for(auto d: dq)cerr << d << " ";
      cerr << endl;
      */
      while(dq[0] != cnt[h]){
        cnt[calc(dq[0])] = -1;
        dq.pop_front();
      }
      dq.pop_front();
      cnt[h] = p[i];
    }
    dq.pb(p[i]);
    if(len == sz(dq))chmax(res, dq[0]);
    else if(len < sz(dq)){
      len = sz(dq);
      res = dq[0];
    }
  }
  cout << res << endl;
  return 0;
}