String cast error

[SomeRiz via Digitalmars-d-learn]

Hi.

My code running:
http://dpaste.dzfl.pl/2183586524df

Output:

SerialNumber
927160020XXXX (X = Some Numbers)

How do I delete "SerialNumber" text?

Example

string SomeRiz = system(a);

I get an error:

b.d(10): Error: cannot implicitly convert expression (system(a)) 
of type int to
string

Later;

string SomeRiz = cast(string)system(a);

I get an error 2:

b.d(10): Error: cannot cast system(a) of type int to string


How do I delete "SerialNumber" text?

I just, want to see the numbers:

927160020XXXX

Sorry for my bad english