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Problem C
Sretan
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.
Input
The first and only line of input contains a positive integer $K$ ($1 \le K \le 10^9$).
Output
The first and only line of output must contain the $K$-th lucky positive integer.
| Sample Input 1 | Sample Output 1 |
|---|---|
1 |
4 |
| Sample Input 2 | Sample Output 2 |
|---|---|
2 |
7 |
| Sample Input 3 | Sample Output 3 |
|---|---|
3 |
44 |