#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (ll i = (s); i < (ll)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (ll i = (ll)(s - 1); i >= (ll)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
bool chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
bool chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") {
    cout << (f ? yes : no) << "\n";
}

struct Sieve {
    vector<int> primes;
    vector<int> _isPrime;
    vector<int> prime_factor_num; // soinsuu no kosuu
    Sieve(int n) : _isPrime(n + 1, 1), prime_factor_num(n + 1, 0) {
        buildPrimes();
    }
    void buildPrimes() {
        _isPrime[0] = _isPrime[1] = 0;
        int n = _isPrime.size();
        REP(i, 2, n) {
            if (_isPrime[i]) {
                primes.push_back(i);
                prime_factor_num[i] = 1;
                for (int j = i + i; j < n; j += i) _isPrime[j] = 0, prime_factor_num[j]++;
            }
        }
    }
    bool isPrime(int i) {
        return _isPrime[i];
    }
};

void solve() {
    int k, n;
    cin >> k >> n;
    Sieve sieve(n + 10);
    deque primes(all(sieve.primes));
    while (primes.front() < k) primes.pop_front();
    while (primes.back() > n) primes.pop_back();

    auto hash = [&](auto self, ll x) -> ll {
        if (x < 10) return x;
        ll nxt = 0;
        while (x > 0) {
            nxt += x % 10;
            x /= 10;
        }
        return self(self, nxt);
    };
    ll ans = primes.front();
    ll len = 1;
    map<ll, ll> mp;
    int r = 0;
    auto init_state = [&](int l) {
        r = l;
    };
    auto judge_r = [&](int l, int r) {
        return mp[hash(hash, primes[r])] == 0;
    };
    auto add_r = [&](int r) {
        mp[hash(hash, primes[r])]++;
    };
    auto update = [&](int l, int r) {
        if (r - l >= len) {
            len = r - l;
            ans = primes[l];
        }
    };
    auto erace_l = [&](int l) {
        mp[hash(hash, primes[l])]--;
    };
    rep(l, primes.size()) {
        if (r < l) init_state(l);
        while (r < primes.size() && judge_r(l, r)) {
            add_r(r);
            r++;
        }
        update(l, r);
        erace_l(l);
    }
    cout << ans << "\n";
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // multi-testcase
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}