def RunLengthEncoding(S):
    res = []
    N = len(S)
    i = 0
    while i < N:
        cnt = 1
        while i < N - 1 and S[i] == S[i + 1]:
            cnt += 1
            i += 1
        res.append((S[i], cnt))
        i += 1
    return res


D = int(input())
S = input() + input()
rle = RunLengthEncoding(S)
ans = 0
for i in range(len(rle)):
    if rle[i][0] == "o":
        ans = max(ans, rle[i][1])
    elif rle[i][1] <= D:
        L = rle[i][1]
        if i:
            L += rle[i - 1][1]
        if i + 1 < 14:
            L += rle[i + 1][1]
        ans = max(ans, L)

print(ans)