CF762A.k-th divisor

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You are given two integers $n$ and $k$ . Find $k$ -th smallest divisor of $n$ , or report that it doesn't exist.

Divisor of $n$ is any such natural number, that $n$ can be divided by it without remainder.

The first line contains two integers $n$ and $k$ ( $1<=n<=10^{15}$ , $1<=k<=10^{9}$ ).

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

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

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.