#include <cstring>
#include <map>
#include <deque>
#include <queue>
#include <stack>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <math.h>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <vector>
#include <set>
#include <list>
#include <climits>
#include <cctype>
#include <bitset>
#include <iostream>
#include <iomanip>
#include <complex>
#include <sys/time.h>


using namespace std;

typedef stringstream ss;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vector<ii> > vvii;
typedef vector<string> vs;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef vector<double> vd;
typedef long double ld;
typedef vector<vector<ll> > grix;
typedef complex<double> point;
typedef complex<long long> pointINT;

int dx[] = { -1, 1, 0, 0, 0, 0 };
int dy[] = { 0, 0, -1, 1, 0, 0 };
int dz[] = { 0, 0, 0, 0, -1, 1 };

int DX[] = { 0, 0, 1, -1, 1, -1, 1, -1 };
int DY[] = { 1, -1, 0, 0, 1, -1, -1, 1 };

double PI = 3.1415926535897932384626433832795;

const ll oo = 1e9 + 1;
const double eps = 1e-6;
const ll mod = 1234567;

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sz(v) ((int)v.size())
#define clr(v, d) memset(v, d, sizeof(v))
#define polar(r,t) ((r)*exp(point(0,(t))))
#define length(a) hypot((a).real(),(a).imag())
#define angle(a) atan2((a).imag() , (a).real())
#define vec(a,b) ((b)-(a))
#define dot(a,b) ((conj(a)*(b)).real())
#define cross(a,b) ((conj(a)*(b)).imag())
#define lengthSqr(a) dot(a,a)
#define rotate(v,t) ((v)*exp(point(0,t)))
#define rotateAbout(v,t,a) (rotate(vec(a,v),t)+(a))
#define reflect(v,m) (conj((v)/(m))*m)
#define dist(a,b) (sqrt(pow((a).real()-(b).real(),2.0)+pow((a).imag()-(b).imag(),2.0)))
#define distsqr(a,b) (pow((a).real()-(b).real(),2.0)+pow((a).imag()-(b).imag(),2.0))
#define normalize(a) ((a)/length(a))
#define ccw(a,b,c) (cross(vec((a),(b)),vec((a),(c)))>=0)
#define collinear(a,b,c) (fabs(cross(vec((a),(b)),vec((a),(c))))<eps)
#define LSOne(S) (S & (-S))
////////////////////////////////////////////////////////////////////////

//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);

bool vis[5000001];
int prime[5000001];
int pal[5000001];

bool ok(int num) {
	string s = "";
	while (num) {
		s += (num % 10);
		num /= 10;
	}
	for (int i = 0; i < sz(s) / 2; i++) {
		if (s[i] != s[sz(s) - 1 - i])
			return false;
	}
	return true;
}

int main() {
	struct timeval t1, t2;
	double elapsedTime;

	// start timer
	gettimeofday(&t1, NULL);
	freopen("in.txt", "r", stdin);
	int mx = 5000000;
	int prime_cnt = 0, pal_cnt = 0;
	vis[0] = vis[1] = true;

	for (int i = 2; i < mx; i++) {
		if (!vis[i]) {
			prime_cnt++;
			for (int j = i + i; j < mx; j += i)
				vis[j] = true;
		}
		prime[i] = prime_cnt;
	}

	for (int i = 1; i < mx; i++) {
		if (ok(i)) {
			pal_cnt++;
		}
		pal[i] = pal_cnt;
	}
	int p, q;
	scanf("%d %d", &p, &q);
	bool ok = false;
	for (int i = mx - 1; i > 0; i--) {
		if (1LL * q * prime[i] <= 1LL * p * pal[i]) {
			printf("%d\n", i);
			ok=true;
			break;
		}
	}
	if(!ok)
	printf("Palindromic tree is better than splay tree\n");
	// stop timer
	gettimeofday(&t2, NULL);

	// compute and print the elapsed time in millisec
	elapsedTime = (t2.tv_sec - t1.tv_sec) * 1000.0;      // sec to ms
	elapsedTime += (t2.tv_usec - t1.tv_usec) / 1000.0;   // us to ms
	cout << elapsedTime << " ms."<<endl;
	return 0;
}