#include"bits/stdc++.h"

using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#define FOR(k,m,n) for(ll (k)=(m);(k)<(n);(k)++)
#define REP(i,n) FOR((i),0,(n))
#define WAITING(str) int str;std::cin>>str;
#define DEBUGING(str) cout<< #str << " " str<<endl

constexpr int INF = (1 << 30);
constexpr ll INFL = (1ll << 60);
constexpr ll MOD = 1000000007;// 10^9+7

//‘fˆö�”•ª‰ð
//in: number
//out: prime numbers
map<int, int> prime_factorization(int n)
{
	map<int, int> res;
	int check = 2;

	while (check*check <= n) {
		if (n%check == 0) {
			n /= check;
			if (res.find(check) == res.end())res[check] = 0;
			res[check]++;
		}
		else {
			check++;
		}
	}
	if (n != 1) {
		if (res.find(n) == res.end())res[n] = 0;
		res[n]++;
	}
	//sort(res.begin(), res.end());
	return res;
}

int count_same_prime(map<int, int> primes, map<int, int> target) {
	int res = 0;
	for (auto itr = primes.begin(); itr != primes.end(); ++itr) {
		int num = itr->first;
		int cnt = itr->second;
		if (target.find(num) == target.end())continue;
		int cnt2 = target[num];
		res += min(cnt, cnt2);
	}
	return res;
}

int count_division(map<int, int> primes) {
	int res = 1;
	for (auto itr = primes.begin(); itr != primes.end(); ++itr) {
		int tmp = (itr->second) + 1;
		res *= tmp;
	}
	return res;
}

int N, K;


int main()
{
	cin >> N >> K;
	int res = -1;
	int score = -1;

	auto target = prime_factorization(N);
	FOR(i, 1, N) {
		if (i == 24) {
			cerr<<endl;
		}
		map<int, int> primes = prime_factorization(i);
		int cnt = count_same_prime(target, primes);
		if (cnt < K)continue;
		int nscore = count_division(primes);
		if (nscore > score) {
			res = i;
			score = nscore;
		}
		
	}

	cout << res << endl;
	//cin>>N;
	return 0;
}