let get_odd lst =
	let rec loop idx acc lst =
		match lst with
		| [] -> acc
		| x :: xs ->
			if idx mod 2 = 1 then loop (idx + 1) (x :: acc) xs
			else loop (idx + 1) acc xs
	in
	loop 0 [] lst

let rec head n lst =
	match lst with
	| [] -> []
	| x :: xs ->
		if n > 0 then x :: head (n - 1) xs
		else []

let () =
	let n = read_int () in
	let a =
		read_line ()
		|> Str.split (Str.regexp " ")
		|> List.map int_of_string
	in
	get_odd a
	|> head n
	|> List.fold_left (+) 0
	|> print_int
	|> print_newline
