Nicholas, a painter is going to paint several new canvases. Nicholas is sure that the canvases will turn out so great that each one will need framing and being hung on the wall. Frames are what Nicholas decided to begin with.

Nicholas has n sticks whose lengths equal a1, a2, ... an. Nicholas does not want to break the sticks or glue them together. To make ah × w-sized frame, he needs two sticks whose lengths equal h and two sticks whose lengths equal w. Specifically, to make a square frame (when h = w), he needs four sticks of the same length.

Now Nicholas wants to make from the sticks that he has as many frames as possible; to be able to paint as many canvases as possible to fill the frames. Help him in this uneasy task. Note that it is not necessary to use all the sticks Nicholas has.

Input

The first line contains an integer n (1 ≤ n ≤ 100) — the number of sticks. The second line contains n space-separated integers. The i-th integer equals the length of the i-th stick ai (1 ≤ ai ≤ 100).

Output

Print the single number — the maximum number of frames Nicholas can make for his future canvases.

Examples
input 
5
2 4 3 2 3
output 
1
input 
13
2 2 4 4 4 4 6 6 6 7 7 9 9
output 
3
input 
4
3 3 3 5
output 
0
晚自习听巨巨们讲思路，原来把成对出现的数归零，最后统计零的对数，如果是奇数还要-1再除二。
第五题选择性忽略，今天就到这了。睡了。。。。