D = int(input())
line1 = input().strip()
line2 = input().strip()
mid = line1 + line2
pre = 'x' * (D + 1)
post = 'x' * (D + 1)
timeline = pre + mid + post

def max_consecutive(s):
    current = 0
    max_o = 0
    for c in s:
        if c == 'o':
            current += 1
            if current > max_o:
                max_o = current
        else:
            current = 0
    return max_o

max_result = 0

for i in range(len(timeline) - D + 1):
    substring = timeline[i:i+D]
    if all(c == 'x' for c in substring):
        new_s = timeline[:i] + 'o' * D + timeline[i+D:]
        current_max = max_consecutive(new_s)
        if current_max > max_result:
            max_result = current_max

print(max_result)