d = gets.strip.to_i
#p d
week1 = gets.strip
week2 = gets.strip
#p week1
#p week2
weeks = week1 + week2
#p weeks

def count_max_o(weeks)
	count_max = 0
	count = 0
	(0...weeks.length).each do |i|
		if weeks[i] == 'o'
			count += 1
		else
			if count > count_max
				count_max = count
			end
			count = 0
		end
		
	end
	if count > count_max
		count_max = count
	end
	#p count_max
	return count_max
end

count_max = 0
count = 0
i = 0
while i < weeks.length do
	weeks1 = weeks.clone
	if weeks[i] == 'o'
		i += 1
		next
	end
	(1..d).each do |j|
		if weeks[i] == 'o'
			break
		else
			weeks1[i] = 'o'
		end
		i += 1
	end
	#p weeks1
	count = count_max_o(weeks1)
	if count > count_max
		count_max = count
	end
	
	i += 1
end
p count_max