There's an easier way: look at the time.
Seconds are even? Type 'f'. Odd? Type 'd'. (Or vice-versa. Or use minutes, if you don't have to do this very often.)
A while ago there was an article (in NYTimes online, I think) about a program that could beat anyone in Rock-Paper-Scissors. That is, it would take a few iterations, and learn your pattern, and do better than chance against you.
It never got any better than chance against me, because I just used the current time as a PRNG.
Edit: Found it. http://www.nytimes.com/interactive/science/rock-paper-scissors.html?_r=0
Edit2: Over 25 rounds, 12-6-7 (win-loss-tie) vs. the "veteran" computer. Try it and post your results! :)
10-5-10 against veteran by trying to predict the computer and occasionally changing levels of recursion.
Second try: 14-16-15 by trying to act randomly (without conciously using an algorithm).
Another monthly installment of the rationality quotes thread. The usual rules apply: