import sys
input=lambda: sys.stdin.readline().rstrip()
d=int(input())
C=input()
C+=input()
C="x"*d+C+"x"*d
def ct(X):
  ret=0
  cur=0
  for i in range(len(X)):
    if X[i]=="o":
      cur+=1
    else:
      ret=max(ret,cur)
      cur=0
  else:
    ret=max(ret,cur)
  return ret
ans=d
for i in range(d+14):
  ans=max(ans,ct(C[:i]+"o"*d+C[i+d]))
print(ans)