#include <bits/stdc++.h>

using namespace std;

const int SZ = 200000;

int dp[200001];

int g(int v)
{
  if(v < 10) return (v);
  return (g(v / 10) + v % 10);
}

int f(int v)
{
  if(~dp[v]) {
    return (dp[v]);
  } else if(v >= 10) {
    return (dp[v] = f(g(v)));
  } else {
    return (dp[v] = v);
  }
}

int main()
{
  bool prime[SZ + 1] = {};
  prime[1] = true;
  for(int i = 2; i * i <= SZ; ++i) {
    if(!prime[i]) {
      for(int j = i + i; j <= SZ; j += i) prime[j] = true;
    }
  }
  memset(dp, -1, sizeof(dp));

  int K, N;
  cin >> K;
  cin >> N;
  vector< int > primes;
  for(int i = K; i <= N; i++) {
    if(!prime[i]) primes.push_back(i);
  }

  int tail = 0, ret = 0, p = 0;
  bool val[10] = {};

  for(int i = 0; i < primes.size(); ++i) {
    while(tail < primes.size() && !val[f(primes[tail])]) {
      val[f(primes[tail])]++;
      ++tail;
    }
    if(ret <= tail - i) {
      p = primes[i];
    }
    ret = max(ret, tail - i);
    val[f(primes[i])] = false;
  }
  cout << p << endl;
}