#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <climits>
#include <functional>
#include <cassert>
#include <numeric>
#define rep(i, n) for(int i = 0; i < (n); i++)
#define per(i, n) for(int i = (n) - 1; i >= 0; i--)
using ll = long long;
#define vi vector<int>
#define vvi vector<vi>
#define vl vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
constexpr int mod = 1000000007;
using namespace std;
template<class T, class U>
bool chmax(T &a, const U &b){ return a < b ? (a = b, 1) : 0; }
template<class T, class U>
bool chmin(T &a, const U &b){ return a > b ? (a = b, 1) : 0; }
struct range_eratosthenes {
  private:
  ll L,R,M;
  static constexpr int Max_range = 1000010; //10^6
  bitset<Max_range> small, large;
  public:
  range_eratosthenes(ll L, ll R) : L(L), R(R), M(sqrt(R)+1){
    assert(M <= Max_range && R - L <= Max_range);
    for(ll i = 2; i < M; i++){
      if(small[i]) continue;
      for(ll j = i+i; j < M; j += i) small[j] = 1;
      for(ll j = max(2LL, (L+i-1)/i)*i; j < R; j += i)
        large[j - L] = 1;
    }
  }
  bool is_prime(const ll &n) const{
    assert(L <= n && n < R);
    return !large[n - L];
  }
};
constexpr inline int calc_hash(int i) noexcept{
  int tot = 0;
  while(i){
    tot += i % 10;
    i /= 10;
  }
  if(tot < 10) return tot;
  return calc_hash(tot);
}
int main(){
  int l,r;
  cin >> l >> r;
  range_eratosthenes ss(l, r+1);
  vi s;
  for(int i = max(l,2); i <= r; i++) if(ss.is_prime(i)) s.push_back(i);
  const int len = (int)s.size();
  vi h(len);
  rep(i, len) h[i] = calc_hash(s[i]);
  int right = 0;
  int cnt[10] = {};
  int ans = 0, val = 0;
  for(int left = 0; left < len; left++){
    while(right < len && !cnt[h[right]]){
      cnt[h[right]]++;
      right++;
    }
    if(ans <= right - left){
      ans = right - left;
      val = s[left];
    }
    if(left == right) right++;
    cnt[h[left]]--;
  }
  cout << val << "\n";
}