How to set CultureInfo.InvariantCulture default?

When I have such piece of code in C#:

double a = 0.003;
Console.WriteLine(a);

It prints "0,003".

If I have another piece of code:

double a = 0.003;
Console.WriteLine(a.ToString(CultureInfo.InvariantCulture));

It prints "0.003".

My problem is that I need a dot as decimal mark but C# makes a comma as default. Besides I don't want to type such a long line of code just for printing out a double variable.