Jonathan Sumabat is having trouble with a math problem during his test. Although normally he would be a model student and take his L, this time he has enlisted your help to write a program that lets him cheat. The problem is this:

How many pairs of prime numbers exist between 1 and n both inclusive such that the difference between the two numbers is exactly 1?

Given ~n~, determine the answer to the above problem for Jonathan Sumabat.

Input Specification

The first line is an integer ~n~ ~(1 \le n \le 10^9)~.

Output Specification

Output the answer to the question stated above.