Problems
Divisibility by 3
Divisibility by 3
Let's consider a sequence 1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011, ... .
Write a program that determines how many elements of this sequence among first n are divisible by three.
Input data
One positive integer n~(1 \le n \le 2^{31} - 1).
Output data
Print one number — the answer to the problem.
Examples
Input example #1
4
Output example #1
2