#include <bits/stdc++.h>
using namespace std;

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    auto solve = [&]() {
        int k, n;
        cin >> k >> n;

        auto isPrime = [&](int n) {
            if (n == 1) { return false; }
            for (int i = 2; i * i <= n; i++) {
                if (n % i == 0) {
                    return false;
                }
            }
            return true;
        };

        vector<int> primes;
        for (int x = k; x <= n; x++) {
            if (isPrime(x)) {
                primes.push_back(x);
            }
        }

        int best = 0, ans = -1;
        vector<int> cnt(9);

        for (int i = 0, j = 0; i < primes.size(); i++) {
            while (j < primes.size() && cnt[primes[j] % 9] == 0) {
                cnt[primes[j++] % 9]++;
            }
            if (j - i >= best) {
                best = j - i;
                ans = primes[i];
            }
            cnt[primes[i] % 9]--;
        }

        cout << ans << '\n';
    };
    
    solve();
    
    return 0;
}