How to overlay 3 functions on one plot using R



I have three functions and a plot code:

f1 <- function(c){0.187*c-0.000236*c^2+0.194*10-0.00330*100-0.000406*10}
f2 <- function(c){0.187*c-0.000236*c^2+0.194*16.53-0.00330*(16.53^2)-0.000406*16.53}
f3 <- function(c){0.187*c-0.000236*c^2+0.194*20-0.00330*400-0.000406*20}

I wish to plot all three of these on the same graph. I currently have:

plot(f1(1:1000), type="l", xlab="x", ylab="y", main="the plot :)")
plot(f2(1:1000), type="l", xlab="x", ylab="y", add = T)

So far this produces just f1 on a plot as opposed to f1 and f2. I believe I am taking the wrong approach because I am producing another plot and trying to add it to a pre-existing plot. I am unsure whether to use geom_line or something similar and just overlay it.

Is there a straight forward way to plot multiple functions and overlay them in the same plot?

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