SRETAN

문제

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.