D = int(input())
week1 = input().strip()
week2 = input().strip()
original = week1 + week2

pre = 'x' * D
post = 'x' * D
S = pre + original + post

max_result = 0

for i in range(len(S)):
    cnt = 0
    j = i
    while j < len(S) and cnt < D and S[j] == 'x':
        cnt += 1
        j += 1
    end = i + cnt - 1
    if cnt == 0:
        continue
    modified = list(S)
    for k in range(i, end + 1):
        modified[k] = 'o'
    current_max = 0
    current = 0
    for c in modified:
        if c == 'o':
            current += 1
            if current > current_max:
                current_max = current
        else:
            current = 0
    if current_max > max_result:
        max_result = current_max

print(max_result)