#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <cstdlib>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional> 
#include <iomanip>
#include <unordered_map>
#include <memory.h>
#include <unordered_set>
#include <fstream>

using namespace std;

int ha[200001];
bool isprime[200001];

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	int K, N;

	cin >> K;
	cin >> N;
	for (int i = 1; i < 10; i++)
	{
		ha[i] = i;
	}
	for (int i = 10; i <= N; i++)
	{
		int val = i;
		int sum = 0;
		while (val > 0)
		{
			sum += (val % 10);
			val /= 10;
		}
		ha[i] = ha[sum];
	}

	vector <int> prime;
	memset(isprime, true, sizeof(isprime));
	isprime[1] = false;
	for (int i = 2; i <= 200000; i++)
	{
		if (isprime[i])
		{
			if (i >= K && i <= N)
			{
				prime.push_back(i);
			}
			for (int j = 2 * i; j <= 200000; j += i)
			{
				isprime[j] = false;
			}
		}
	}

	//슬라이딩 윈도우
	int res = N;
	int val = 0;
	set <int> S;
	int cnt = 0;
	int L = 0;
	int R = 0;
	int n = prime.size();
	while (1)
	{
		//cout << L << ' ' << R << ' ' << res << ' ' << val << ' ' << cnt << '\n';
		if (L >= n && R >= n)
		{
			break;
		}
		if (R < n)
		{
			if (S.find(ha[prime[R]]) == S.end())
			{
				cnt++;
				S.insert(ha[prime[R]]);
				R++;
			}
			else
			{
				if (val <= cnt)
				{
					val = cnt;
					res = prime[L];
				}
				S.erase(ha[prime[L]]);
				L++;
				cnt--;
			}
		}
		else
		{
			if (val <= cnt)
			{
				val = cnt;
				res = prime[L];
			}
			S.erase(ha[prime[L]]);
			L++;
			cnt--;
		}
	}

	cout << res << '\n';

	return 0;
}