#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

int K, N;
bool np[200001];
vector<int> ps;
vector<int> phs;

int hsh(int v) {
	if (v < 10) return v;
	int w = 0;
	while (v > 0) {
		w += v % 10;
		v /= 10;
	}
	return hsh(w);
}

int main(int argc, char **argv) {
	cin >> K >> N;
	CLEAR(np);
	np[0] = np[1] = true;
	FOR(i, 2, N + 1) {
		if (np[i]) continue;
		for (int j = i * 2; j <= N; j += i) np[j] = true;
	}
	FOR(i, K, N + 1) if (!np[i]) ps.push_back(i);
	REP(i, ps.size()) phs.push_back(hsh(ps[i]));
	map<int, int> prv;
	int len = 0, mlen = 0, s = 0, mi = -1;
	REP(i, phs.size()) {
		int h = phs[i];
		if (prv.count(h) > 0 && prv[h] >= s) {
			s = prv[h] + 1;
			prv[h] = i;
			len = i - s + 1;
		}
		else {
			prv[h] = i;
			++len;
			if (len >= mlen) {
				mlen = len;
				mi = s;
			}
		}
	}
	if (len >= mlen) mi = s;
	cout << ps[mi] << endl;
	return 0;
}