Even Sum Pair Counter

You are given a list of n integers. Your task is to calculate the number of distinct pairs (i, j) (with 1 ≤ i < j ≤ n) such that the sum of the i-th and j-th numbers is even.

Recall that the sum of two integers is even if both integers are even or both are odd.

Formally, if we denote the list as a₁, a₂, …, aₙ, you need to count the number of pairs (i, j) satisfying (1 \le i < j \le n) and (a_i + a_j \equiv 0 \pmod{2}).

inputFormat

The input is given via standard input (stdin).

The first line contains an integer n (the number of elements).

The second line contains n space-separated integers representing the elements of the list.

outputFormat

Output a single integer to standard output (stdout) representing the number of pairs (i, j) such that the sum of the elements at these indices is even.## sample

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