N = gets.to_i
S = gets.chomp.chars.sort.reverse
T = 'yuki'
queue = S

ans = 0
stock = []

5.times do |i|
  next_que = []
  next_stock = []

  until queue.empty?
    s = queue.shift

    if i == 4
      if stock.size > 0
        ans += 1
        stock.shift
      end

      next
    end

    if T[i] > s
      next_que << s
      next
    end

    if T[i] < s
      if i == 0
        ans += 1
      elsif stock.size > 0
        ans += 1
        stock.shift
      end
    else
      if i == 0
        next_stock << s
      elsif stock.size > 0
        str = stock.shift
        str << s
        next_stock << str
      else
        next_que << s
      end
    end
  end

  queue = next_que
  stock = next_stock
end

puts ans