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Problems

Morning exercises

Morning exercises

Time limit 1 second
Memory limit 128 MiB

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 data

Sequence of n (n10^6) positive integers, giving the colour of a T-shirt (the colour is a number from 0 to 9).

Output data

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

Examples

Input example #1
0 3 6 3 0 0 1
Output example #1
2