class Calc0204
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @d = args.shift.first.to_i
    @s = args.map(&:first).join
  end

  def run
    if @d == 0
      @s.scan(/o+/).map(&:size).max || 0
    else
      s = ('x' * @d) + @s + ('x' * @d)
      os = [0] + s.scan(/o+/).map(&:size) + [0]
      xs = s.scan(/x+/).map(&:size)

      xs.flat_map.with_index { |x, i|
        if x <= @d
          [os[i] + x + os[i + 1]]
        else
          [os[i] + @d, os[i + 1] + @d]
        end
      }.max || 0
    end
  end
end

puts Calc0204.new(STDIN.readlines).run if __FILE__ == $0