### Problem Statement

A number is preprime if it has exactly 4 positive integer divisors. For example, 6 is preprime because its divisors are 1, 2, 3, and 6. The integers 6, 8, 10, 14 form the beginning of an infinite sequence of preprime numbers. Find the n-th element of this sequence, where n is a 1-based index.

### Definition

 Class: PreprimeNumbers Method: nthNumber Parameters: int Returns: int Method signature: int nthNumber(int n) (be sure your method is public)

### Constraints

-n will be between 1 and 1000000, inclusive.

### Examples

0)

 `2`
`Returns: 8`
 The beginning of an infinite sequence of preprime numbers is: 6, 8, 10, 14, ... The second number is 8.
1)

 `4`
`Returns: 14`
 The beginning of an infinite sequence of preprime numbers is: 6, 8, 10, 14, ... The fourth number is 14.
2)

 `24`
`Returns: 77`
3)

 `43765`
`Returns: 193539`

#### Problem url:

http://www.topcoder.com/stat?c=problem_statement&pm=6083

#### Problem stats url:

http://www.topcoder.com/tc?module=ProblemDetail&rd=9987&pm=6083

Mike Mirzayanov

#### Testers:

PabloGilberto , brett1479 , Olexiy , marian

#### Problem categories:

Search, Simple Math