Description

It is known that $4$ and $7$ are lucky digits, and other digits are not lucky digits. If an integer contains only lucky digits in its decimal representation, then this integer is lucky. You need to find the $k$-th lucky positive integer.

Input Format

The input contains one line.

One line with one integer $k$, with the meaning as described above.

Output Format

The output contains one line.

One line with one integer, which is the answer.

1

4

2

7

3

44

Hint

Explanation for Sample Input/Output 1

Because we are looking for positive integers, the first one must be the number $4$.

Constraints

For $100\%$ of the testdata, $1 \leq k \leq 10^9$.

Note

This problem is translated from COCI2010-2011 CONTEST #1 T3 SRETAN.

Translated by ChatGPT 5