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

// エラトステネスの篩(nは1以上, 素数列挙のみならi*i<=nで良い) O(nloglogn)
vector<bool> sieve(int n) {
  vector<bool> x(n + 1, true);
  x.at(0) = x.at(1) = false;
  for (int i = 2; i <= n; i++) {
    if (x.at(i)) {
      for (int j = 2 * i; j <= n; j += i) x.at(j) = false;
    }
  }
  return x;
}

// 各桁の数の和
int digitSum(int x) {
  int sum = 0;
  while (x > 0) {
    sum += x % 10;
    x /= 10;
  }
  if (sum <= 9) return sum;
  else return digitSum(sum);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  
  int k, n;
  cin >> k >> n;
  
  vector<bool> p = sieve(n);
  vector<int> primes;
  for (int i = k; i <= n; i++) {
    if (p[i]) primes.emplace_back(i);
  }
  
  vector<int> hash(primes.size());
  for (int i = 0; i < primes.size(); i++) hash[i] = digitSum(primes[i]);
  
  int ans = -1, len = 0, it = 0;
  set<int> s;
  for (int i = 0; i < hash.size(); i++) {
    while (true) {
      if (it < hash.size() && s.find(hash[it]) == s.end()) {
        s.insert(hash[it]);
        it++;
      }
      else {
        break;
      }
    }
    if (it - i >= len){
      len = max(len, it - i);
      ans = primes[i];
    }
    s.erase(hash[i]);
  }
  
  cout << ans << '\n';
}