A number is considered perfect if its digits sum up to exactly 10. Given a positive integer n, return the n-th perfect number.

Write a function `solve`

that have the following parameter(s):

1.) *a = an integer*

**Example**

Input:

`3`

Output:

`7`

**Explanation**

The input is `3`

and if we add `7`

then its sum up will be exactly 10.

**Constraints**

• The value of an integer should be greater than 0 and less than 10000.