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.
\InputFile
One positive integer $n~(1 \le n \le 2^{31} - 1)$.
\OutputFile
Print one number --- the answer to the problem.
Input example #1
4
Output example #1
2