D = int(input())
C = list(input())
C += list(input())
C = ["x"]*D + C +["x"]*D
ans = 0
for i in range(14+D+1):
    if C[i]=="x":
        A = C[:]
        cnt = 0
        while cnt<D and A[cnt+i]=="x":
            A[cnt+i] = "o"
            cnt += 1
        cnt = 0
        for j in range(14+2*D):
            if A[j]=="o":
                cnt += 1
            else:
                ans = max(ans,cnt)
                cnt = 0
print(ans)