[R] two Kaplan-Meier Curves in one plot

[Verena Hoffmann]

Hello!
Maybe someone is able to help me here:

I want to compare the survival probabilities of patients treated with 
two different  kinds of medicine.
So I did the     KM <- survfit(Surv(Time, Status), type="Kaplan-Meier")
                 plot(KM)
for each group seperatly. But now I want to compare both treatments and 
have both Kaplan-Meier Curves in one plot.
HOW CAN I DO THAT?
I tried add=TRUE, but that didn't work.

Thousand thanks in advance,
Verena