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.