Little Prohor is a war victim. She lives in HellOnEarth.
She loves reading book. Her situation can't stop her from gaining knowledge. Besides, she also inspires her friends and they too started to love reading books.
There, 3 children can share a book. So, 2 books are enough for 6 children.
We are planning to send them a few books.
Help us calculate the minimum number of books to buy for those children .
Input will contain an integer N ( 1 ≤ N ≤ 230 , where N is the number of children).
Print the number of books required for the children.