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();
        Prime[] used = new Prime[10];
        TreeSet<Prime> primes = new TreeSet<Prime>();
        int max = 0;
        int maxNumber = 0;
        for (int i = k; i <= n; i++) {
            if (!isPrime(i)) {
                continue;
            }
            Prime p = new Prime(i);
            if (used[p.hashCode()] == null) {
                used[p.hashCode()] = p;
                primes.add(p);
            } else {
                Prime x = used[p.hashCode()];
                used[p.hashCode()] = null;
                while (primes.lower(x) != null) {
                    Prime tmp = primes.lower(x);
                    primes.remove(x);
                    x = tmp;
                    used[x.hashCode()] = null;
                }
                primes.remove(x);
                used[p.hashCode()] = p;
                primes.add(p);
            }
            if (max <= primes.size()) {
                max = primes.size();
                maxNumber = primes.first().number;
            }
        }
        System.out.println(maxNumber);
    }
    
    static class Prime implements Comparable<Prime> {
        int number;
        int hash;
        
        public Prime(int number) {
            this.number = number;
            this.hash = getHash(number);
        }
        
        public int hashCode() {
            return hash;
        }
        
        public boolean equals(Object o) {
            Prime another = (Prime) o;
            return number == another.number;
        }
        
        public int compareTo(Prime another) {
            return number - another.number;
        }
        
        private int getHash(int x) {
            while (x >= 10) {
                int y = x;
                x = 0;
                while (y > 0) {
                    x += y % 10;
                    y /= 10;
                }
            }
            return x;
        }
    }
    
    static boolean isPrime(int x) {
        if (x < 2) {
            return false;
        }
        for (int i = 2; i <= Math.sqrt(x); i++) {
            if (x % i == 0) {
                return false;
            }
        }
        return true;
    }
}