#include <bits/stdc++.h>

#define REP(i, x, n) for(int i = x; i < (int)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define F first
#define S second
#define mp make_pair

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

const int MAX = 200000;

bool isPrime[MAX + 1];

void sieve(int N){
  for(int i = 0; i <= N; i++) {
    isPrime[i] = true;
  }
  
  isPrime[0] = isPrime[1] = false;

  for(int i = 2; i <= N; i++) {
    if(!isPrime[i]) continue;
    for(int j = i + i; j <= N; j += i) {
      isPrime[j] = false;
    }
  }
}

int conv(int v) {
  while(v >= 10) {
    int res = 0;
    while(v) {
      res += v % 10;
      v /= 10;
    }
    v = res;
  }
  return v;
}

int main() {
  // ios_base::sync_with_stdio(false);
  int K, N;
  cin >> K >> N;

  sieve(N);

  vector<P> prime;
  for(int i = K; i <= N; i++) {
    if(isPrime[i]) {
      prime.push_back(P(i, conv(i)));
    }
  }

  int maxLen = 0;
  int maxPrime = 0;
  int idx = 0;
  set<int> st;

  for(int i = 0; i < prime.size(); i++) {
    if(st.count(prime[i].S) == 0) {
      st.insert(prime[i].S);
      if(maxLen <= i - idx + 1) {
        maxLen = i - idx + 1;
        maxPrime = prime[idx].F;
      }
    }
    else {
      while(st.count(prime[i].S)) {
        st.erase(prime[idx].S);
        idx++;
      }
      st.insert(prime[i].S);
      if(maxLen <= i - idx + 1) {
        maxLen = i - idx + 1;
        maxPrime = prime[idx].F;
      }
    }
  }

  cout << maxPrime << endl;
  
  return 0;
}