greater than question

Hopefully someone has done this and has an easy answer. I know that I can do what I need with a LOT of code, but am trying to come up with something a little shorter that 50 lines of code. Here is the problem. I have 4 variables that each have a number in them. I need to find which one has the highest number. I then just need to do something with that number. If two or more have the same "highest" number, than I need to do the same thing with them. So...... $a=5 $b=1 $c=5 $d=3 $a and $c are the highest number. I need to run something on those two variables. Thanks in Advance Steve