import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int k = sc.nextInt();
    int n = sc.nextInt();
    ArrayList<Integer> prime = new ArrayList<Integer>();
    ArrayList<Integer> F = new ArrayList<Integer>();
    for(int i = k; i <= n; i++) {
      if(isP(i)) prime.add(i);
    }
    Collections.sort(prime);
    for(int i = 0; i < prime.size(); i++) {
      F.add(f(prime.get(i)));
    }
    int right = 0;
    int ans = 0;
    int len = 0;
    int[] kosuu = new int[100];
    for(int i = 0; i < prime.size(); i++) {
      int[] b = kosuu;
      b[f(prime.get(i))]++;
      while(right < prime.size() - 1) {
        if(b[prime.get(right + 1)] > 0) {
          break;
        } else {
          b[prime.get(right + 1)]++;
          right++;
        }
      }
      int t = right - i + 1;
      if(len <= t) {
        ans = prime.get(i);
        len = t;
      }
    }
  }

  public static boolean isP(int n) {
    int p = 0;
    for(int i = 2; (i * i) <= n; i++) {
      if((n % i) == 0) p++;
    }
    if(p == 0) return true;
    return false;
  }

  public static int f(int n) {
    if(n < 10) return n;
    int q = 0;
    for(int i = 0; (int)Math.pow(10, i) <= n; i++) {
      int t = n / (int)Math.pow(10, i);
      q += (t % 10);
    }
    return f(q);
  } 
}