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C - Socks

Score : $300$ points

Problem Statement

You have $N$ socks. The color of the $i$-th sock is $A_i$.

You want to perform the following operation as many times as possible. How many times can it be performed at most?

• Choose two same-colored socks that are not paired yet, and pair them.

Constraints

• $1\leq N \leq 5\times 10^5$
• $1\leq A_i \leq 10^9$
• All values in the input are integers.

Input

The input is given from Standard Input in the following format:

$N$

$A_1$ $A_2$ $\dots$ $A_N$

Output

Print an integer representing the answer.

6
4 1 7 4 1 4

2

You can do the operation twice as follows.

• Choose two socks with the color $1$ and pair them.
• Choose two socks with the color $4$ and pair them.

Then, you will be left with one sock with the color $4$ and another with the color $7$, so you can no longer do the operation. There is no way to do the operation three or more times, so you should print $2$.

1
158260522

0

10
295 2 29 295 29 2 29 295 2 29

4