k-th divisor

Description:

Input:

The first line contains two integers n and k (1 ≤ n ≤ 10¹⁵, 1 ≤ k ≤ 10⁹).

Output:

If n has less than k divisors, output -1.

Otherwise, output the k-th smallest divisor of n.

Sample Input:

4 2

Sample Output:

2

Sample Input:

5 3

Sample Output:

-1

Sample Input:

12 5

Sample Output:

6

Note:

In the first example, number 4 has three divisors: 1, 2 and 4. The second one is 2.

In the second example, number 5 has only two divisors: 1 and 5. The third divisor doesn't exist, so the answer is -1.