문제

Author: Goran Gašić

Digits 4 and 7 are lucky, while all others are unlucky. An integer is lucky if it contains only lucky digits in decimal notation. We would like to know the K-th lucky positive integer.

입력

The first and only line of input contains a positive integer K (1 ≤ K ≤ 109).

출력

The first and only line of output must contain the K-th lucky positive integer.

예제 입력 1

1

예제 출력 1

4

예제 입력 2

2

예제 출력 2

7

예제 입력 3

3

예제 출력 3

44