#include <bits/stdc++.h>
#define int long long
#define uint unsigned int
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = (n); i >= 0; --i)
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORR(i, a, b) for (int i = (a); i >= (b); --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define SZ(a) ((int)(a).size())
#define PB(a) push_back(a)
#define EB(...) emplace_back(__VA_ARGS__)
#define MP(a, b) make_pair(a, b)
#define MT(...) make_tuple(__VA_ARGS__)
#define Bit(n) (1LL << (n))
using namespace std;
using pii = pair<int, int>;
template <class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template <class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
const int MOD = 1000000007;
const int INF = 1LL << 30;
const double EPS = 1e-10;

const int MAX_N = 1000010;
vector<int> prime;
bool is_prime[MAX_N];

int sieve(int n) {
  for (int i = 0; i <= n; i++) is_prime[i] = true;
  for (int i = 2; i <= n; i++) {
    if (is_prime[i]) {
      prime.push_back(i);
      for (int j = i*i; j <= n; j += i) is_prime[j] = false;
    }
  }
  return prime.size();
}

int K, N;
vector<int> v, ps;

int calc(int x) {
  if (x / 10 == 0) return x;
  int r = 0;
  while (x) {
    r += x % 10;
    x /= 10;
  }
  return calc(r);
}

signed main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  
  cin >> K >> N;
  sieve(N);
  for (int p : prime) {
    if (K <= p && p <= N) {
      v.EB(calc(p));
      ps.EB(p);
    }
  }
  int l = 0, r = 0;
  int n = SZ(v);
  int mx = 0;
  int ans = -1;
  set<int> st;
  while (l < n) {
    while (r < n && st.count(v[r]) == 0) {
      st.insert(v[r]);
      r++;
    }
    if (r-l >= mx) {
      ans = ps[l];
      mx = r-l;
    }
    st.erase(v[l]);
    l++;
  }
  cout << ans << endl;

  return 0;
}