Count Same Height Pairs

You are given a sequence of buildings with their respective heights. Your task is to determine the number of distinct pairs of buildings that have the same height.

Formally, given an integer \( N \) and a list of \( N \) integers \( h_1, h_2, \dots, h_N \), count the number of pairs \( (i, j) \) with \( 1 \leq i < j \leq N \) such that \( h_i = h_j \). This can be computed using the combination formula: if a certain height appears \( c \) times then it contributes \( \binom{c}{2} = \frac{c(c-1)}{2} \) pairs.

Input is provided via stdin and your answer should be printed to stdout.

inputFormat

The first line of input contains a single integer \( N \) representing the number of buildings. The second line contains \( N \) space-separated integers representing the heights of the buildings.

outputFormat

Output a single integer representing the number of distinct pairs of buildings that share the same height.

## sample

6
3 3 3 2 2 1

4

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