d = int(input())
c = list(input())
c += list(input())
cc = [c[:] for j in range(15 - d)]
cnt = 0
ans = 0

for j in range(15 - d):
    for k in range(j,j + d):
        cc[j][k] = "o"
    cnt = 0

    for i in range(14):
        if cc[j][i] == "o":
            cnt += 1
        ans = max(ans, cnt)
        if cc[j][i] == "x":
            cnt = 0

print(ans)