Competitions

# Preparation for Azercell Cup, 5 - 7 classes

# 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.

#### Input

Sequence of **n** (**n** ≤ `10`

) positive integers, giving the colour of a T-shirt (the colour is a number from ^{6}**0** to **9**).

#### Output

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

Input example #1

0 3 6 3 0 0 1

Output example #1

2