#coding: utf-8
##yuki_204

d=int(raw_input())
s1=raw_input()
s2=raw_input()

s='x'*d+s1+s2+'x'*d
res=0
for i in xrange(len(s)):
 maxl=0
 temp=d
 for j in xrange(len(s)):
  if j>=len(s):
   break
  if s[j]=='o':
   maxl+=1
   if j>=i:
    temp=0
  elif j>=i and temp>0:
   temp-=1
   maxl+=1
  else:
   maxl=0
  res=max(maxl,res)
  
print res