Help: extrac the first entry for each component of a list

Dear All,
I would like to know, beside writing a function and then apply it to a list, or using a for loop, whether there is a one-line command to do the following.
Suppose we have a list, each of whose components are numeric:

a <- vector("list",3)
a[[1]] <-c(1,2)
a[[2]] <-c(3,4)
a[[3]] <- c(5,6)
a

[[1]]
[1] 1 2

[[2]]
[1] 3 4

[[3]]
[1] 5 6

Target: I would like to extract from each of its components the first entry and store them into a vector, ie, to extract 1 from a[[1]], 3 from a[[2]], 5 from a[[3]], and store 1,3,5 into a vector without using for loops.
Thank you,
Chee
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