#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif

int main() {
    int64_t l, r;
    cin >> l >> r;

    auto hash = [](int64_t x) -> int64_t {
        while (10 <= x) {
            int64_t y = 0;
            for (; x; x /= 10) {
                y += x % 10;
            }
            x = y;
        }
        return x;
    };

    vector<bool> is_prime(r + 1, true);
    is_prime[0] = false;
    is_prime[1] = false;
    for (int64_t i = 2; i * i <= r; i++) {
        if (is_prime[i]) {
            for (int64_t j = 2 * i; j <= r; j += i) {
                is_prime[j] = false;
            }
        }
    }

    vector<int64_t> ps;
    for (int64_t i = l; i <= r; i++) {
        if (is_prime[i]) {
            ps.push_back(i);
        }
    }

    vector<int64_t> qs(ps.size());
    for (int64_t i = 0; i < ps.size(); i++) {
        qs[i] = hash(ps[i]);
    }

    int64_t max_len = 0;
    int64_t start = 0;

    map<int64_t, int64_t> mp;
    for (int64_t i = 0, j = 0; i < qs.size(); i++) {
        while (mp.contains(qs[i])) {
            mp[qs[j]]--;
            if (mp[qs[j]] == 0) {
                mp.erase(qs[j]);
            }
            j++;
        }

        mp[qs[i]]++;

        if (max_len <= i - j) {
            max_len = i - j;
            start = j;
        }
    }

    cout << ps[start] << endl;

    return 0;
}