#include <bits/stdc++.h>

using namespace std;

class Prime {
private:
  vector<long long> div;
  
public:
  Prime(long long n = 0) {
    for (long long i = 0; i <= n; ++i) div.emplace_back(i);
    for (long long i = 2; i <= n / i; ++i) if (div[i] == i) {
      for (long long j = i * i; j <= n; j += i) div[j] = i;
    }
  }
  
  bool isPrime(long long n) const {
    if (n <= 1) return false;
    if (n < (long long)div.size()) return div[n] == n;
    for (long long i = 2; i <= n / i; ++i) if (n % i == 0) return false;
    return true;
  }
  
  vector<long long> factor(long long n) const {
    vector<long long> res;
    for (long long i = 2; i <= n / i && n >= (long long)div.size(); ++i) {
      while (n % i == 0) {
        res.emplace_back(i);
        n /= i;
      }
    }
    if (n >= max((long long)div.size(), 2ll)) {
      res.emplace_back(n);
    } else {
      while (n > 1) {
        res.emplace_back(div[n]);
        n /= div[n];
      }
    }
    sort(res.begin(), res.end());
    return res;
  }
  
  vector<long long> primeFactor(long long n) const {
    vector<long long> res;
    for (long long i = 2; i <= n / i && n >= (long long)div.size(); ++i) {
      if (n % i) continue;
      res.emplace_back(i);
      while (n % i == 0) n /= i;
    }
    if (n >= max((long long)div.size(), 2ll)) {
      res.emplace_back(n);
    } else {
      while (n > 1) {
        long long d = div[n];
        res.emplace_back(d);
        while (n % d == 0) n /= d;
      }
    }
    sort(res.begin(), res.end());
    return res;
  }

  vector<long long> divisor(long long n) const {
    vector<long long> res;
    for (long long i = 1; i <= n / i; ++i) {
      if (n % i == 0) {
        res.emplace_back(i);
        if (i != n / i) res.emplace_back(n / i);
      }
    }
    sort(res.begin(), res.end());
    return res;
  }
};

class DoublePointer {
private:
  int n;

protected:
  int front, back;

  virtual bool valid(int) = 0;
  virtual void pop(int) = 0;
  virtual void push(int) = 0;
  
public:
  DoublePointer(int n) : n(n) {}

  void solve() {
    for (front = 0, back = 0; front < n;) {
      if (back < n && valid(back)) {
        push(back);
        ++back;
      } else {
        if (front < back) pop(front);
        else ++back;
        ++front;
      }
    }
  }
};

class UniqueHash : public DoublePointer {
private:
  vector<int> v;
  set<int> s;

  bool valid(int back) {
    return s.count(v[back]) == 0;
  }

  void pop(int front) {
    s.erase(v[front]);
  }

  void push(int back) {
    s.insert(v[back]);
    if (mx <= s.size()) {
      mx = s.size();
      res = this->front;
    }
  }

public:
  size_t mx = 0, res;

  UniqueHash(const vector<int>& v) : DoublePointer(v.size()), v(v) {}
};

int main() {
  int k, n;
  cin >> k >> n;
  Prime prime(n);
  vector<int> p;
  for (int i = k; i <= n; ++i) {
    if (prime.isPrime(i)) p.emplace_back(i);
  }
  auto v = p;
  for (int& i : v) {
    while (i >= 10) {
      string s = to_string(i);
      i = accumulate(s.begin(), s.end(), 0) - '0' * s.size();
    }
  }
  UniqueHash uh(v);
  uh.solve();
  cout << p[uh.res] << endl;
}