You are given an array of integers. Your task is to create pairs of them, such that every created pair has the same sum. This sum is not specified, but the number of created pairs should be the maximum possible. Each array element may belong to one pair only. Write a function

class Solution public int
solution (int[] A); }

that, given an array A consisting of N integers, returns the maximum possible number of pairs with the same sum.

Examples:
1. Given A = [1, 9, 8, 100, 2], the function should return 2. The pairs are (A[0]. A[1]) and (A[2], A[4]); the sum of each pair is 10.
2. Given A = [2, 2, 2, 3], the function should return 1. Although, for instance, A[0]+A[1] = A[0]+A[2], the pairs (A[0], A[1]) and (A[0], A[2]) cannot exist at the same time, because they both contain a common element, A[0].