#include <bits/stdc++.h>

using namespace std;

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

bool prime[200010];

int mhash(int x){
  if(x < 10) return x;
  int res = 0;
  while(x > 0){
	res += x % 10;
	x /= 10;
  }
  return mhash(res);
}

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

  int N, M; cin >> N >> M;
  fill(prime, prime+200010, true);
  prime[0] = prime[1] = false;
  for(int i=2;i*i<=M;++i)
	if(prime[i])
	  for(int j=i+i;j<=M;j+=i)
		prime[j] = false;
  vector<int> primes;
  FOR(i,N,M+1) if(prime[i]) primes.PB(i);
  
  int ans = 0, p = 0;
  REP(i,SZ(primes)){
	vector<bool> use(10, false);
	FOR(j,i,SZ(primes)){
	  int h = mhash(primes[j]);
	  if(use[h]){
		break;
	  }
	  else if(j-i >= ans){
		ans = j - i;
		p = primes[i];
	  }
	  use[h] = true;
	}
  }
  cout << p << endl;

  return 0;
}