How to implement the following code without goto and unnecessary code complexity?

namespace Test
{
    static class Program
    {
        bool keyA = false;
        bool keyB = false;
        // ...
        static void Main(string[] args)
        {
            foreach (string arg in args)
            {
                switch (arg.ToLowerInvariant())
                {
                    case "-a":
                        if(keyA) break;
                        keyA = true;
                        // do here also what the A key requires
                        break;
                    case "-b":
                        if(keyB) break;
                        keyB = true;
                        // do here also what the B key requires
                        goto case "-a"; // key B includes the action of key A
                    // ...
                }
            }
        }
    }
}

The only thing that suggests itself is to duplicate the lines of code from key A to key B or use stuffing everything into methods, but this doesn’t look convenient and compact to view.