Partition Sequence into Pairs

Given a sequence of integers, determine whether it is possible to partition the sequence into pairs such that the sum of the integers in each pair equals a given target value \( k \). Note that the sequence must contain an even number of elements. For a valid partition, every pair \( (a, b) \) must satisfy \( a + b = k \).

Your program should read from standard input and output the result to standard output.

inputFormat

The first line contains two integers \( n \) and \( k \) separated by a space, where \( n \) is the number of elements in the sequence and \( k \) is the target sum for each pair.

The second line contains \( n \) integers representing the sequence, separated by spaces.

outputFormat

Output a single line containing possible if it is possible to partition the sequence into pairs such that every pair sums to \( k \); otherwise, output impossible.

4 7
1 6 2 5

possible