#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int n, k;
    cin >> n >> k;

    int r = -1;
    ll m = 0;
    for (int i = 1; i < n; i++) {
        int t = i, s = n, y = 0;
        ll c = 1;
        for (int j = 2; j * j <= n; j++) {
            int h = 0;
            while (t % j == 0) {
                if (s % j == 0) s /= j, y++;
                t /= j, h++;
            }
            c *= h + 1;
        }
        if (s > 1 && t > 1 && s % t == 0) y++;
        if (t > 1) c *= 2;
        if (y >= k && c > m) {
            m = c;
            r = i;
        }
    }

    cout << r << endl;

    return 0;
}