J. Parallelograms
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

There are n sticks, the i-th of which has length ai. Alex wants to assemble from them as many parallelograms as possible simultaneously, with each stick used at most in one parallelogram. What maximal number of parallelograms is it possible to assemble?

Input

The first line contains a single integer n (1 ≤ n ≤ 200000) — the number of sticks.

The second line contains n integers ai (1 ≤ ai ≤ 200000) — the lengths of sticks.

Output

Output a single integer — the maximal number of parallelograms that is possible to assemble.

Examples
Input
4
1 2 1 2
Output
1
Input
12
1 3 5 7 1 3 5 7 1 3 5 7
Output
2