#include <bits/stdc++.h>
using namespace std;

#define repu(i, a, b) for (int i = (a); i < (b); ++i)
#define repd(i, a, b) for (int i = (a); i > (b); --i)
#define mem(a, x) memset(a, x, sizeof(a))
#define all(a) a.begin(), a.end()
#define uni(a) a.erase(unique(all(a)), a.end())

typedef long long ll;
const int MOD = 1000000007;

template<class T, class U> inline T tmin(T a, U b) {return (a < b) ? a : b;}
template<class T, class U> inline T tmax(T a, U b) {return (a > b) ? a : b;}
template<class T, class U> inline void amax(T &a, U b) {if (b > a) a = b;}
template<class T, class U> inline void amin(T &a, U b) {if (b < a) a = b;}
template<class T> inline T tabs(T a) {return (a > 0) ? a : -a;}
template<class T> T gcd(T a, T b) {while (b != 0) {T c = a; a = b; b = c % b;} return a;}

const int N = 200005;
int k, n;
vector<int> primes;
int dp[N], maxi[N], pos[N];
bool is_prime[N];

void init() {
	mem(is_prime, true);
	repu(i, 2, n + 1) {
		if (is_prime[i]) {
			if (i >= k) primes.push_back(i);
			for (int j = i + i; j <= n; j += i) is_prime[j] = false;
		}
	}
}

int hash_func(int x) {
	if (dp[x] >= 0) return dp[x];
	int nxt = 0;
	while (x) {
		nxt += x % 10;
		x /= 10;
	}
	dp[x] = hash_func(nxt);
	return dp[x];
}

int main(int argc, char *argv[]) {
	ios_base::sync_with_stdio(false);
	
	cin >> k >> n;
	
	init();
	
	mem(dp, -1); mem(pos, -1);
	repu(i, 0, 10) dp[i] = i;
	repu(i, 10, n + 1) dp[i] = hash_func(i);
	
	int m = primes.size();
	int ret = primes[m - 1], len = 1;
	maxi[m - 1] = 1;
	pos[dp[primes[m - 1]]] = m - 1;
	repd(i, m - 2, -1) {
		maxi[i] = 1 + maxi[i + 1];
		if (pos[dp[primes[i]]] != -1) {
			amin(maxi[i], pos[dp[primes[i]]] - i);
		}
		pos[dp[primes[i]]] = i;
		if (maxi[i] > len) {
			len = maxi[i], ret = primes[i];
		}
	}
	
	cout << ret << endl;
	
	return 0;
}