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# System prepended metadata

title: Medium - 2

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# Medium - 2

A teacher has been assigned a class with **N** students of different grade levels.

In each training session, the teacher can teach **2** or **3** students of the same grade level.

Your task is to find the minimum number of training sessions needed in order to teach all of the students in the class.

Write a program that reads a number **N**, and **N** space-separated numbers representing the grade levels of students, and prints a single integer representing the minimum number of training sessions needed in order to teach all of the students in the class.

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#### Input

The first line of input contains an integer representing `N`.
The second line of input contains `N` space-separated integers representing the grade levels of students.

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#### Output

The output should be a single line containing an integer that is the minimum number of training sessions needed in order to teach all of the students in the class.

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#### Explanation

For example, if `N = 10`, grade levels of students are `2 2 2 4 4 5 5 5 5 5`,

- In the first training session, the teacher teaches students from grade 2.
- In the second training session, the teacher teaches students from grade 4.
- In the third training session, the teacher teaches 3 students from grade 5.
- In the fourth training session, the teacher teaches 2 students from grade 5.

The output should be **4**.
