# 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. --- #### 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. --- #### 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. --- #### 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**.