.cs

using System;
using System.Globalization;

public class Program
{
  public static void Main()
  {
    var lowerHello = "hello world";
     Console.WriteLine(CultureInfo.CurrentCulture.TextInfo.ToTitleCase(lowerHello));
      
    var regularHello = "Hello world";
     Console.WriteLine(CultureInfo.CurrentCulture.TextInfo.ToTitleCase(regularHello));
      
    var capsHello = "HELLO WORLD";
     Console.WriteLine(CultureInfo.CurrentCulture.TextInfo.ToTitleCase(capsHello));
  }
}