iterated sum

Hi,
Try:

?x[-1]+x[-length(x)]

A.K.

x<-c(1,4,9,20,3,7)
i want to get a serie c(5,13,29,23,10).
y <- c()
for (i in 2:length(x)){
? ?  y[i-1] <- x[i-1]+x[i]}

is there more simple way to get?
??? [[alternative HTML version deleted]]

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