Given the length of n segments. What is the maximum number of squares can be constructed? Each side of a square must be constructed from only one segment.
The first line contains the number of segments n (1 ≤ n ≤
106). The second line contains n integers - the length of segments with values no more than 100.
Print the maximum number of squares that can be constructed from the given segments.
9 2 2 4 2 3 2 1 2 4