#include"bits/stdc++.h"
//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
typedef long long ll;
const ll mod = 200000;

int n, k;

bool pdp[mod];
vector<int> makeprime() {
	vector<int> ret;
	for (int i = 2; i < k+1; i++)
	{
		if (pdp[i]) continue;
		if(i>=n&&i<=k)ret.push_back(i);
		for (int j = i + i; j < k+1; j += i)
		{
			pdp[j] = true;
		}
	}
	return ret;
}

int has(int a) {
	int count = 0;
	if (a / 10 == 0)return a;
	while (a / 10 != 0) {
		count += a % 10;
		a /= 10;
	}
	count += a;
	return has(count);
}

int main() {
	cin >> n >> k;
	auto prime = makeprime();
	int ma = 0;
	int ans = 0;
	rep(i, 0, prime.size()) {
		int count = 0;
		bool hash[10] = {};
		int rem=0;
		for (int j = i; j < prime.size(); j++) {
			if (hash[has(prime[j])] != 1&&prime[j]<=k) {
				if (count == 0)rem = prime[j];
				count += 1;
				hash[has(prime[j])] = 1;
			}
			else break;
			if (count > ma) { ma = count; ans = rem; }
			else if (count == ma) { ans = max(ans, rem); }
		}
	}
	print(ans);
	return 0;
}