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Morning exercises

Morning exercises

In the morning, many students do their exercises. According to established tradition, the students dance in the branded T-shirts. During the first three days of the camp, schoolchildren and teachers noticed that a couple who dances in identical T-shirts looks more aesthetically better. Therefore before the exercises, they decided first to put pairs of children in identical T-shirts, and then the remaining ones. The excellent student Seryozha wanted to know what the largest number of aesthetic pairs can be formed from everyone who came to morning exercises.


Sequence of n (n106) positive integers, giving the colour of a T-shirt (the colour is a number from 0 to 9).


Print the number of aesthetic pairs that can be made up.

Time limit 1 second
Memory limit 128 MiB
Input example #1
0 3 6 3 0 0 1
Output example #1
Вікно у Європу
Площа об'єднання прямокутників (ізотетичних)