# Task
We know that some numbers can be split into two primes. ie. `5 = 2 + 3, 10 = 3 + 7`. But some numbers are not. ie. `17, 27, 35`, etc.. 
Given a positive integer `n`. Determine whether it can be split into two primes. If yes, return the maximum product of two primes. If not, return `0` instead.
# Input/Output
`[input]` integer `n`
A positive integer. 
`0 ≤ n ≤ 100000`
`[output]` an integer
The possible maximum product of two primes. or return `0` if it's impossible split into two primes.
# Example
For `n = 1`, the output should be `0`.
`1` can not split into two primes
For `n = 4`, the output should be `4`.
`4` can split into two primes `2 and 2`. `2 x 2 = 4`
For `n = 20`, the output should be `91`.
`20` can split into two primes `7 and 13` or `3 and 17`. The maximum product is `7 x 13 = 91`
def prime_product(n, sieve=[False, False, True, True]):
    for x in range(len(sieve), n+1):
        sieve.append(x % 2 and all(x % p for p in range(3, int(x ** .5) + 1, 2) if sieve[p]))
    return next((p * (n - p) for p in range(n//2, 1, -1) if sieve[p] and sieve[n - p]), 0)
def prime_product(n, sieve=[False, False, True, True]):
    for x in range(len(sieve), n+1):
        sieve.append(x % 2 and all(x % p for p in range(3, int(x ** .5) + 1, 2) if sieve[p]))
    return next((p * (n - p) for p in range(n//2, 1, -1) if sieve[p] and sieve[n - p]), 0)