# 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 |