Replace good with bad

Given a string, write a method that replaces every word 'good' with 'bad'. Assume that words to be replaced may consist of mixed cases (gOod, baD, etc.).
Expected input and output
ReplaceGoodWithBad("gOOd") → "good" ReplaceGoodWithBad("so b@d") → "so b@d"
using System;
using System.Text.RegularExpressions;

namespace CSharpExercises.Exercises.Regular_expressions
{
    class ReplaceGoodWithBadTask
    {
        public static string ReplaceGoodWithBad(string word)
        {
            string output = string.Empty;
            return output = Regex.Replace(word, @"((G|g)(O|o){2}(D|d))", "bad");
        }

        public static void Main()
        {
            Console.WriteLine(ReplaceGoodWithBad("Very GoOd"));         // Very bad
            Console.WriteLine(ReplaceGoodWithBad("GooDgOOdGOODgood"));  // badbadbadbad
            Console.WriteLine(ReplaceGoodWithBad("Not so g00d"));       // Not so g00d
        }
    }
}