#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define out(a) cout << a << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)

vector<pair<int, int> > prime_factorize(int n) {
    int tmp = n;
    vector<pair<int, int> > v;
    for (int i = 2; i * i <= n; ++i) {
        int cnt = 0;
        while (tmp % i == 0) {
            tmp /= i;
            cnt++;
        }
        if (cnt) v.eb(i, cnt);
    }
    if (tmp != 1) v.eb(tmp, 1);
    return v;
}

vector<int> all_divisor_catch(int n) {
    vector<int> res;
    for (int i = 1; i * i <= n; i++) {
        if (n % i == 0) {
            res.push_back(i);
            if (i != n / i) res.push_back(n / i);
        }
    }
    return res;
}

vector<int> sieve() {
    const int MAX_N = 100001 + 1;
    vector<int> v(MAX_N, 0);
    v[0] = v[1] = 1;
    for (int i = 2; i * i <= MAX_N; ++i) {
        int tmp = 2;
        while (tmp * i <= MAX_N) {
            v[tmp++ * i] = 1;
        }
    }
    vector<int> v2;
    rep(i, SZ(v)) if (v[i] == 0) v2.eb(i);
    return v2;
}

int gcd(int a, int b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}
int main() {
    
    int n, k; cin >> n >> k;
    pii ans = pii(-1, 0);
    rep3(i, 1, n) {
        //nとk個以上共通の素因数もつか
        auto a = prime_factorize(gcd(n, i));
        int sum = 0;
        rep(i, SZ(a)) sum += a[i].S;
        if (sum < k) continue;
        //iの約数の個数
        chmax(ans, pii(SZ(all_divisor_catch(i)), -i));
        
    }
    out(-ans.S);
}