/* ---------- STL Libraries ---------- */
// IO library
#include <cstdio>
#include <fstream>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>
#include <random>
#include <cstring>

// container library
#include <array>
#include <bitset>
#include <deque>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
#include <stack>

/* ---------- Namespace ---------- */
using namespace std;

/* ---------- Type ---------- */
using ll = long long;
#define int ll
#define P pair<ll, ll>

/* ---------- Constants  */
const double PI = 3.141592653589793238462643383279;
const ll MOD = 1e9 + 7;
const int INF = 1LL << 55;

map<int, int> prime_factor(int n) {
    map<int, int> ret;
    for (int i = 2; i * i <= n; i++) {
        while (n % i == 0) {
            ret[i]++;
            n /= i;
        }
    }

    if (n != 1) ret[n] = 1;
    return move(ret);
};

signed main() {
    int N, K;
    cin >> N >> K;

    map<int, int> n_factors = prime_factor(N);
    int mx = -1;
    int ret = -1;

    for (int i = 1; i < N; i++) {
        map<int, int> i_factors = prime_factor(i);
        int common_factor_n = 0;
        int div_n = 1;
        for (auto it = i_factors.begin(); it != i_factors.end(); it++) {
            common_factor_n += min(it->second, n_factors[it->first]);
            div_n *= 1 + it->second;
        }
        if (common_factor_n >= K) {
            if (div_n > mx) {
                mx = div_n;
                ret = i;
            }
        }
    }

    cout << ret << endl;

    return 0;
}