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

using Int32 = int_fast32_t;
using Word32 = uint_fast32_t;
using Int = int_fast64_t;
using Word = uint_fast64_t;
using Int128 = __int128_t;
using Word128 = __uint128_t;
using VInt = vector<Int>;
using VVI = vector<VInt>;
using VWord = vector<Word>;
using VVW = vector<VWord>;
using VS = vector<string>;
using VVS = vector<VS>;
using VB = vector<bool>;
using VVB = vector<VB>;
using PII = pair<Int,Int>;
using PWW = pair<Word,Word>;
using VPII = vector<PII>;
using VPWW = vector<PWW>;

#define SZ(x) ((Int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define rep(i,n) for(Int i=0, i##_len=(n); i<i##_len; ++i)
#define reps(i,n) for(Int i=0, i##_len=(n); i<=i##_len; ++i)
#define Range(i,a,b) for(Int i=a; i<=(Int)(b); i++)
#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(),(x).rend()
#define pb push_back
#define eb emplace_back


const Int inf = 200005;
bool primes[inf];

VInt make_prime() {
  VInt ret;
  for (Int i = 2; i < inf; i++) {
    if (primes[i]) continue;
    ret.pb(i);
    for (Int j = i * i; j < inf; j += i) primes[j] = true;
  }
  return ret;
}

Int make_hash(Int a) {
  Int ret = 0;
  while (a > 0) {
    ret += a % 10;
    a /= 10;
  }
  if (ret >= 10) return make_hash(ret);
  return ret;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  auto prime = make_prime();
  Int K, N;
  cin >> K >> N;
  Int j = 0;
  while (prime[j] < K) j++;
  VInt dp(1000, 0);
  Int ans = 0;
  Int ans_len = 0;
  rep(i,SZ(prime)) {
    if (prime[i] < K) continue;
    if (prime[i] > N) break;
    Int ihash = make_hash(prime[i]);
    dp[ihash]++;
    while (dp[ihash] > 1) {
      Int jhash = make_hash(prime[j]);
      j++;
      dp[jhash]--;
    }
    if (i - j + 1 >= ans_len) {
      ans = prime[j];
      ans_len = i - j + 1;
    }
  }
  cout << ans << endl;
  return 0;
}