#include <iostream>
#include <vector>

std::vector<int> primes(int n) {
    std::vector<bool> is_prime(n + 1, true);
    is_prime.at(0) = false;
    is_prime.at(1) = false;
    std::vector<int> res;
    for (int i = 2; i < n + 1; i++) {
        if (is_prime.at(i)) {
            res.push_back(i);
            for (int j = i * 2; j < n + 1; j += i) {
                is_prime.at(j) = false;
            }
        }
    }
    return res;
}

int calc_hash(int p) {
    int hash = p;
    while (hash >= 10) {
        int new_hash = 0;
        while (hash != 0) {
            new_hash += hash % 10;
            hash /= 10;
        }
        hash = new_hash;
    }
    return hash;
}

int main() {
    int K, N;
    std::cin >> K;
    std::cin >> N;
    std::vector<int> primes_candidate;

    for (auto &p: primes(N)) {
        if (p < K) { continue; }
        primes_candidate.push_back(p);
    }

    std::vector<int> exist_indices(10, -1);
    int ans;
    int l = 0, M = 0;
    for (int r = 0; r < primes_candidate.size(); r++) {
        int hash = calc_hash(primes_candidate.at(r));
        if (exist_indices.at(hash) != -1
            && l < exist_indices.at(hash) + 1) {
            l = exist_indices.at(hash) + 1;
        }
        exist_indices.at(hash) = r;
        if (M <= r - l) {
            ans = primes_candidate.at(l);
            M = r - l;
        }
    }
    std::cout << ans << std::endl;
}