#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>
#include <cstring>

using namespace std;

int mhash(int x) {
  while (x%10 != x) {
    int t = 0;
    for (int i = x; i != 0; i/=10) t += i%10;
    x = t;
  }
  return x;
}

int main() {
  int k, n;
  cin >> k >> n;
  bool not_prime[n+1];
  memset(not_prime, false, sizeof(not_prime));
  not_prime[1] = true;
  for (int i = 2; i <= n; i++) {
    for (int j = i+i; j <= n; j+=i) {
      not_prime[j] = true;
    }
  }

  //  for (int i = 0; i <= n; i++) cout << i << ": " << not_prime[i] << endl;

  vector <int> memo;
  for (int i = k; i <= n; i++) if (!not_prime[i]) memo.push_back(i);

   // for (int i = 0; i < memo.size(); i++) cout << mhash(memo[i]) << endl;

  int ans, maxi = 0;
  bool used[10]; memset(used, false, sizeof(used));
  used[mhash(memo[0])] = true;
  for (int l = 0, r = 1; r < memo.size(); r++) {
    if (used[mhash(memo[r])] || r == memo.size()-1) {
      if (maxi <= r-l) {
	maxi = r-l;
	ans = memo[l];
      }
      while (mhash(memo[l]) != mhash(memo[r])) {
	used[mhash(memo[l])] = false;
	l++;
      }
      l++;
      if (l < memo.size() && maxi <= r-l+1) {
	maxi = r-l+1;
	ans = memo[l];
      }
    }
  }

  if (!maxi) {
    cout << memo[memo.size()-1] << endl;
  }else {
    cout << ans << endl;
  }
}