n=input()
s="x"*n+raw_input()+raw_input()+"x"*n
#print s
#print max(len(i)for i in s.split("x"))
m=0
for i in range(len(s)):
	t=list(s)
	for j in range(i,min(i+n,len(s))):
		if t[j]=="o":
			break
		t[j]="o"
	#print "".join(t)
	m=max(m,max(len(i)for i in "".join(t).split("x")))
print m