#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
using namespace std;

#define FOR(i, s, e) for (int i = (s); i <= (e); i++)

vector<int> prime;

int hash_[2000001];

int K;
int N;

int s = -1;
int e = -1;

int result = 0;
int cou;

int main()
{
    cin >> K;
    cin >> N;
    for (int i = 2; i <= N; i++)
    {
        bool pri = true;
        for (int j = 0; j < prime.size() && pri; j++)
        {
            if (i % prime[j] == 0)
                pri = false;
        }

        if (pri)
        {
            prime.push_back(i);
            if (i >= K && s == -1)
                s = prime.size() - 1;
            if (i <= N)
            {
                e = prime.size() - 1;
            }
        }
    }

    FOR(i, 1, N)
    {
        if (i <= 9)
            hash_[i] = i;
        else
        {
            int tot = 0;
            int x = i;
            while (x != 0)
            {
                tot += x % 10;
                x /= 10;
            }
            hash_[i] = hash_[tot];
        }
    }
    int start = e;
    bool used[10];
    fill(used, used + 10, false);
    for (int i = e; i >= s; i--)
    {
        int h = hash_[prime[i]];
        if (used[h] == false)
        {
            used[h] = true;
        }
        else
        {
            if (cou < start - i)
            {
                cou = start - i;
                result = prime[i + 1];
            }
            i = start;
            start--;
            fill(used, used + 10, false);
        }
    }
    cout << result << endl;
    return 0;
}