#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <deque>
#include <list>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>

using namespace std;

bool prime[200001];
int app[10];
long int K, N;
vector<int> nums;

int main() {
	long int i, j;
	int len = 0;
	int maxlen = 0;
	int prevlen = 0;
	int ret;

	cin >> K;
	cin >> N;

	for (i = 2; i <= N; i++) prime[i] = true;
	for (i = 2; i <= N; i++) {
		if (prime[i]) {
			for (j = 2*i; j <= N; j += i) {
				prime[j] = false;
			}
		}
	}
	for (i = N; i >= K; i--) {
		if (prime[i]) {
			int ci = i;
			while (ci >= 10) {
				int sum = 0;
				for (j = 5; j >= 0; j--) {
					int temp = floor(ci/pow(10,j));
					sum += temp;
					ci -= temp * pow(10,j);
				}
				ci = sum;
			}

			for (j = 0; j < 10; j++) {
				app[j]++;
				if (j == ci) {
					len = app[j];
					app[j] = 0;
				}
			}

			if (len > prevlen + 1) len = prevlen + 1;

			cout << i << ":" << ci << ":" << len << endl;

			if (maxlen < len) {
				maxlen = len;
				ret = i;
			}
			
			prevlen = len;

		}
	}

	cout << ret << endl;

	return 0;
}