Subtract from the previous row R [duplicate]

Question

I have a dataframe like so:

df <- data.frame(start=c(5,4,2),end=c(2,6,3))

start end
    5   2
    4   6
    2   3

And I want the following result:

start end diff
    5   2 
    4   6    1
    2   3   -1

Essentially it is:

end[2] (second row) - start[1] = 6-5=1

and end[3] - start[2] = 3-4 = -1

What is a good way of doing this in R?