N = gets.to_i
S = gets.chomp

open = close = set = 0
a = []
S.chars{|c|
  if c == ?(
    open += 1
  else
    if open > 0
      open -= 1
      set += 1
    else
      close += 1
    end
  end
  a << [set, open, close]
}
a.sort_by!{|set, open, close|
  [-(open - close), -set]
}
open_cnt = close_cnt = cnt = 0
a.each_with_index{|(set, open, close), i|
  close_cnt += close if i != 0
  open_cnt += open if i != a.size - 1
  cnt += set
}
p (cnt + [close_cnt, open_cnt].min)*2