// bundled by scripts/bundle_header.py

// ---- begin: main.cpp
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

// ---- begin: include/math/linear_sieve.hpp

// 線形篩
// primes[0..prime_cnt): 素数リスト, lp[i]: i の最小素因数 (lp[0] = lp[1] = -1)
template <int N>
struct LinearSieve {
    int lp[N + 1]{};
    int primes[N]{};
    int prime_cnt = 0;

    LinearSieve() {
        lp[0] = lp[1] = -1;
        for (int i = 2; i <= N; i++) {
            if (lp[i] == 0) {
                lp[i] = i;
                primes[prime_cnt++] = i;
            }
            for (int j = 0; j < prime_cnt && primes[j] <= lp[i] && (long long)i * primes[j] <= N; j++) {
                lp[i * primes[j]] = primes[j];
            }
        }
    }
};
// ---- end: include/math/linear_sieve.hpp

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    constexpr int N = 200200;
    LinearSieve<N> sieve;
    int cnt = sieve.prime_cnt;

    int n, k;
    cin >> n >> k;
    int res = 0, ans = 0;

    auto f = [](int x) -> int {
        while (x > 10) {
            int y = 0;
            while (x > 0) {
                y += x % 10;
                x /= 10;
            }
            x = y;
        }
        return x;
    };

    swap(n, k);
    for (int i = 0; i < cnt; i++) {
        if (sieve.primes[i] > n) break;
        if (sieve.primes[i] < k) continue;
        int bit = 0;
        for (int j = i; j < cnt; j++) {
            if (sieve.primes[j] > n) {
                if (res <= j - i) {
                    res = j - i;
                    ans = sieve.primes[i];
                }
                break;
            }
            int x = f(sieve.primes[j]);
            if ((1 << x) & bit) {
                if (res <= j - i) {
                    res = j - i;
                    ans = sieve.primes[i];
                }
                break;
            }
            bit |= 1 << x;
        }
    }
    cout << ans << "\n";
}
// ---- end: main.cpp