d = gets.chomp.to_i
c1 = gets.chomp
c2 = gets.chomp
c = c1 + c2
#puts c
max_day = 0
def count_max_day(weeks)
	count_max_day = 0
	count_day = 0
	weeks.each_char do |day|
		if day == 'x'
			count_day = 0
		else
			count_day += 1
			count_max_day = [count_day, count_max_day].max
		end
	end
	count_max_day
end
if d == 0
	puts count_max_day(c)
	exit
end
max_day = 0
weeks = 'o' * d + c
#puts weeks
max_day = [count_max_day(weeks), max_day].max
#p max_day
weeks = c + 'o' * d
#puts weeks
#p max_day
max_day = [count_max_day(weeks), max_day].max
#p c.length
index = 0
while index < c.length && c[index] == 'x'
#p index
index += 1
end
if index <= d
	weeks = 'o' * (d - index) + c
	max_day = [count_max_day(weeks), max_day].max
end
(index...c.length).each do |i|
	next if c[i] == 'o' 
	seq_days = 1
	count_day = 0
	(1...d).each do |j|
		break if i + j >= c.length || c[i + j] == 'o'
		seq_days += 1
	end
	weeks = c[0, i] + ("o" * seq_days) + c[i + seq_days..-1]
	if i + seq_days == c.length
		weeks += 'o' * (d - seq_days)		
	end
	if weeks.length == 15
#		weeks += 'o'	
	end
#	puts weeks
	max_day = [count_max_day(weeks), max_day].max
end
puts max_day