#include <cassert>
#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define RFOR(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)

#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define show(x) cout << #x << " = " << x << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define pii pair<int, int>
#define vi vector<int>

using namespace std;
template <class S, class T>
ostream& operator<<(ostream& o, const pair<S, T>& p)
{
    return o << "(" << p.first << "," << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& vc)
{
    o << "sz = " << vc.size() << endl
      << "[";
    for (const T& v : vc)
        o << v << ",";
    o << "]";
    return o;
}
typedef long long ll;

#define MAX 200001
vector<ll> prime;
vector<int> hs;
bool check[MAX];
int N;
int K;
int mask[10];

bool can()
{
    rep(i, 10)
    {
        if (mask[i] >= 2) {
            return false;
        }
    }
    return true;
}

ll ok(int length)
{
    for (int i = 0; i < 10; i++) {
        mask[i] = 0;
    }

    if (hs.size() < length) {
        return -1;
    }
    for (int i = 1; i <= length; i++) {
        mask[hs[hs.size() - i]]++;
    }
    if (can()) {
        return prime[hs.size() - length];
    }
    int head = (int)(hs.size() - length) - 1;
    int tail = hs.size() - 1;
    for (; head >= 0; head--, tail--) {
        mask[hs[tail]]--;
        mask[hs[head]]++;
        if (can()) {
            return prime[head];
        }
    }
    return -1;
}

int main()
{
    cin >> K >> N;
    rep(i, N + 1)
    {
        check[i] = true;
    }
    check[0] = check[1] = false;
    for (ll i = 2; i <= N; i++) {
        if (check[i]) {
            for (ll j = 2; i * j <= N; j++) {
                check[i * j] = false;
            }
        }
    }
    for (ll i = K; i <= N; i++) {
        if (check[i]) {
            prime.pb(i);
            hs.pb(i % 9);
        }
    }
    ll ans;
    for (int l = 7; l >= 1; l--) {
        if (ok(l) != -1) {
            ans = ok(l);
            break;
        }
    }
    cout << ans << endl;

    return 0;
}