Sales by Match

Source: HackerRank

Version: Phuoc Hung OJ Extended

Problem

There are $n$ socks. Sock $i$ has color ID $a_i$. Two socks form a pair if and only if their colors are equal, and each sock can be used in at most one pair.

If color $v$ occurs $f_v$ times, it contributes

pairs. Compute the total number of pairs.

Input

• The first line contains $n$.
• The second line contains $a_1,a_2,\ldots,a_n$.

Output

Print the total number of pairs.

Subtasks

Subtask 1 (20 points): $1\le n\le 20$ and $1\le a_i\le 20$.

Subtask 2 (30 points): $1\le n\le 50$ and $1\le a_i\le 50$.

Subtask 3 (50 points): $1\le n\le 100$ and $1\le a_i\le 100$.

Example

Input

9
10 20 20 10 10 30 50 10 20

Output

3

Explanation

Color 10 makes two pairs and color 20 makes one pair, for a total of three.