Divisibility by 3#7330

Divisibility by 3

1 second

128 megabytes

Very easy

Let's consider a sequence $1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011, \dots$ 1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011, \ldots .

Write a program that determines how many elements of this sequence among first $n$ are divisible by three.

Input

One positive integer $n (1 \leq n \leq 2^{31} - 1)$ n~(1 \le n \le 2^{31} - 1).

Output

Print one number — the answer to the problem.

Examples

Example 1

Loading

1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011, \dots

n (1 \leq n \leq 2^{31} - 1)