CF977C.Less or Equal

You are given a sequence of integers of length $n$ and integer number $k$ . You should print any integer number $x$ in the range of $[1; 10^9]$ (i.e. $1 \le x \le 10^9$ ) such that exactly $k$ elements of given sequence are less than or equal to $x$ .

Note that the sequence can contain equal elements.

If there is no such $x$ , print "-1" (without quotes).

The first line of the input contains integer numbers $n$ and $k$ ( $1 \le n \le 2 \cdot 10^5$ , $0 \le k \le n$ ). The second line of the input contains $n$ integer numbers $a_1, a_2, \dots, a_n$ ( $1 \le a_i \le 10^9$ ) — the sequence itself.

Print any integer number $x$ from range $[1; 10^9]$ such that exactly $k$ elements of given sequence is less or equal to $x$ .

If there is no such $x$ , print "-1" (without quotes).

In the first example $5$ is also a valid answer because the elements with indices $[1, 3, 4, 6]$ is less than or equal to $5$ and obviously less than or equal to $6$ .

In the second example you cannot choose any number that only $2$ elements of the given sequence will be less than or equal to this number because $3$ elements of the given sequence will be also less than or equal to this number.