Count Unique Pairs with Given Sum

You are given a list of integers and a target integer (k). Your task is to count the number of unique pairs ((a, b)) in the list such that (a + b = k). A pair is considered unique if the set ({a, b}) is distinct, meaning that ((a, b)) is treated the same as ((b, a)). For example, given the list ([1, 2, 3, 4, 5]) and (k = 5), the valid pairs are ((1, 4)) and ((2, 3)), so the answer is 2.

inputFormat

The input is read from standard input. The first line contains two integers (n) and (k), where (n) is the number of elements in the list and (k) is the target sum. The second line contains (n) space-separated integers representing the elements of the list.

outputFormat

Output a single integer to standard output representing the count of unique pairs whose sum is exactly (k).## sample

5 5
1 2 3 4 5

2