Problem 43639. Counting candies

In a classroom of 'n' children, every even numbered child gets one big candy and every odd numbered child gets two small candies. Count the total number of candies 'x' that one should bring to the class.

For example, if there are n = 10 children in the class, the first child gets two candies, second child gets one candy, third child gets two candies and so on. Total number of candies required is x = 15.