class Yukicoder
  def initialize
    @d = gets.to_i

    @week = "x" * 14
    @week += gets.chomp
    @week += gets.chomp
    @week += "x" * 14
    answer = 0

    0.upto(@week.size-1) do |i|
      temp = @week.dup

      set_renkyu(i)
      answer = [answer, get_renkyu].max

      @week = temp.dup
    end

    puts answer
  end

  def set_renkyu(i)
    count = 0

    while @week[i] == 'x' && count < @d
      @week[i] = 'o'
      i += 1 
      count += 1
    end
  end

  def get_renkyu
    renkyu = 0
    max_renkyu = 0

    @week.chars do |ch|
      if ch == 'o'
        renkyu += 1
      else
        max_renkyu = [max_renkyu, renkyu].max
        renkyu = 0
      end
    end

    max_renkyu = [max_renkyu, renkyu].max

    max_renkyu
  end
end

Yukicoder.new