from itertools import permutations as perm
d = int(input())
s = list(input() + input())
c = []
for i in range(14):
	if s[i] == 'x':
		c.append(i)
ans = 0
for p in perm(c, d):
	for i in p:
		s[i] = 'o'
	i = 0
	while i < 14:
		j = i
		while j < 14 and s[j] == 'o':
			j += 1
		ans = max(ans, j - i)
		i = j + 1
	for i in p:
		s[i] = 'x'
print(ans)