A1409.[COCI-2010_2011-contest1]#3 SRETAN
普及/提高-
COCI
通过率：0%
时间限制：1.00s
内存限制：128MB
题目描述
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.
输入格式
The first and only line of input contains a positive integer K (1 ≤ K ≤ 10^9).
输出格式
The first and only line of output must contain the K-th lucky positive integer.
输入输出样例
输入#1
1
输出#1
4
输入#2
2
输出#2
7
输入#3
3
输出#3
44