Problem Description

Given that $4$ and $7$ are lucky digits, and other digits are not lucky digits. An integer is considered lucky if it contains only lucky digits in its decimal representation. You need to find the $k$-th lucky positive integer.

Input Format

The input consists of a single line.

A single integer $k$, as described in the problem.

Output Format

The output consists of a single line.

A single integer, representing the answer.

Sample Input and Output

Sample Input #1

1

Sample Output #1

4

Sample Input #2

2

Sample Output #2

7

Sample Input #3

3

Sample Output #3

44

Notes

Sample Input and Output 1 Explanation

Since it is a positive integer, the first one must be the digit $4$.

Data Size and Constraints

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

Note

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

见题面 Input 部分

见题面 Output 部分