You don't even need the namespace or the usings if you just want to print hello world either.
class HelloWorld
{
static void Main()
{
System.Console.Write("Hello world!");
}
}
Try it online:
https://tio.run/##Sy7WTc4vSv3/PzknsbhYwSM1Jyc/PL8oJ4WrmktBob...