#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()
/*
	No.6 使いものにならないハッシュ

	しゃくとり法

	蟻本 p135〜
*/
using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const int MAX_N = 200008;

bool p[MAX_N];
vector<int> prime;

void sieve(void ){
	fill (p, p+MAX_N, true );
	p[0] = false;
	p[1] = false;
	
	for (int i = 2; i < MAX_N; i++ ){
		if (p[i] ){
			for (int j = 2*i; j < MAX_N; j += i ){
				p[j] = false;
			} // end for
		} // end if
	} // end for

	prime.clear();
	for (int i = 2; i < MAX_N; i++ ){
		if (p[i] ) prime.push_back (i );
	} // end for
}

int digit_sum (int n ){

	if (n < 10 ) return n;

	int res = 0;
	while (n > 0 ){
		res += n%10;
		n /= 10;
	} // end while

	return digit_sum (res );
}

int main()
{
	sieve();
	ios_base::sync_with_stdio(0);
	int K, N; cin >> K >> N;

	int min_prime_ind = -1;
	rep (i, prime.size() ){
		if (prime[i] >= K ){
			min_prime_ind = i;
			break;
		} // end if
	} // end for

	int max_prime_ind = -1;
	rep (i, prime.size() ){
		if (prime[i] <= N ){
			max_prime_ind = i;
		}else{
			break;
		} // end if
	} // end for

	int res = 0;
	int ans = 0;
	for (int l = min_prime_ind; l <= max_prime_ind ; l++ ){
		int curr = 0;
		set<int> same; same.clear();
		for (int r = l; r <= max_prime_ind; r++ ){
			int sum = digit_sum (prime[r] );
//			cerr << "prime[r]: " << prime[r] << " sum: " << sum << endl;
			if (!same.count (sum ) ){
				same.insert (sum );
			}else{
				break;
			} // end if
			curr = r - l + 1;
		} // end for
		if (res <= curr ){
			res = curr;
			ans = prime[l];
		} // end if
	} // end for

	cout << ans << endl;

	return 0;
}