n = int(input())

s1 = input()
s2 = input()
s = "x"*14+s1+s2+"x"*14


vacation_length = [0 for i in range(len(s))]

max_v = 0
for i in range(len(s)):
	v = 0
	if s[i] == "x":

		#print(i)
		for j in range(i,len(s)):
			if s[j] == "x":
				v += 1
			else:
				vacation_length[i] = v
				break
	v = min(v,n)
	sv = s[:i] + "o"*v + s[i+v:]
	if "o" in sv:
		max_v = max(max_v,(max([len(i) for i in sv.split("x") if i != ""])))