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