#include <iostream>
#include <cmath>
#include <vector>
#include <utility>
#include <queue>
#include <map>
#include <string>
#include <cstring>
#include <algorithm>
#define INF 114514

using namespace std;

typedef pair<int,int> P;

int myhash(int n){
	if(n/10 == 0)return n;

	int sum = 0;
	while(n!=0){
		sum += n%10;
		n /= 10;
	}
	return myhash(sum);
}

vector<int> eratosthenes_sieve(int n){
	vector<int> table(n+1);
	vector<int> prime_list;

	for(int i=2;i<n+1;i++){
		if(table[i] == 0){
			prime_list.push_back(i);
			for(int j=i+i;j<n+1;j+=i)
				table[j] = 1;
		}
	}
	return prime_list;
}


int main(void){
	int k,n;
	cin >> k >> n;
	vector<int> arr = eratosthenes_sieve(n);

	bool used[10] = {0};
	vector<int> width(n+1);


	int haba = 0;
	for(int r=0,l=0;r<arr.size() && arr[r] <= n;r++){
		if(arr[r] < k){
			l++;
			continue;
		}
		while(used[myhash(arr[r])]){
			used[myhash(arr[l])] = false;
			l++;haba--;
			width[arr[l]] = haba;
		}

		used[myhash(arr[r])] = true;
		haba++;
		width[arr[l]] = haba;
	}

	int ret = 0,var = 0;
	for(int i=0;i<arr.size();i++){
		//cout << arr[i] << ":" << myhash(arr[i]) << ":"<< width[arr[i]] << endl;
		if(width[arr[i]] >= var){
			var = width[arr[i]];
			ret = arr[i];
		}
	}
	cout << ret << endl;

	return 0;
}