#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

struct Sieve {
  int n;
  vector<int> f, primes;
  Sieve(int n = 1) : n(n), f(n + 1) {
    f[0] = f[1] = -1;
    for (ll i = 2; i <= n; ++i) {
      if (f[i]) continue;
      primes.push_back(i);
      f[i] = i;
      for (ll j = i * i; j <= n; j += i) {
        if (!f[j]) f[j] = i;
      }
    }
  }
  //素数判定
  bool isPrime(int x) { return f[x] == x; }

  //((ll)素因数,指数)列挙
  vector<pair<ll, int>> factorL(ll x) {
    vector<pair<ll, int>> res;
    for (int p : primes) {
      int y = 0;
      while (x % p == 0) x /= p, ++y;
      if (y != 0) res.emplace_back(p, y);
    }
    if (x != 1) res.emplace_back(x, 1);
    return res;
  }

  // int素因数列挙
  vector<int> factorList(int x) {
    vector<int> res;
    while (x != 1) {
      res.push_back(f[x]);
      x /= f[x];
    }
    return res;
  }
  //((int)素因数,指数)列挙
  vector<P> factor(int x) {
    vector<int> fl = factorList(x);
    if (fl.size() == 0) return {};
    vector<P> res(1, P(fl[0], 0));
    for (int p : fl) {
      if (res.back().first == p) { res.back().second++; }
      else {
        res.emplace_back(p, 1);
      }
    }
    return res;
  }
} prime(200005);

int main() {
  int k, n;
  cin >> k >> n;
  vector<int> a, b;
  auto f = [&](int x) {
    while (x >= 10) {
      int y = x;
      x = 0;
      while (y) {
        x += y % 10;
        y /= 10;
      }
    }
    return x;
  };
  for (auto p : prime.primes) {
    if (k <= p && p <= n) {
      a.push_back(f(p));
      b.push_back(p);
    }
  }

  int m = sz(a);
  set<int> s;
  int l = 0, r = 0;
  int ans = 0, len = 0;
  for (; l < m;) {
    while (r < m && !s.count(a[r])) { s.insert(a[r++]); }
    if (len <= r - l) {
      ans = b[l];
      len = r - l;
    }
    s.erase(a[l++]);
  }
  cout << ans << endl;
  return 0;
}