D = int(input())
line1 = input().strip()
line2 = input().strip()

original = line1 + line2
extended = 'x' * D + original + 'x' * D

max_streak = 0
n = len(extended)

for i in range(n - D + 1):
    substr = extended[i:i+D]
    if substr.count('x') != D:
        continue
    new_str = extended[:i] + 'o' * D + extended[i+D:]
    current = 0
    max_current = 0
    for c in new_str:
        if c == 'o':
            current += 1
            max_current = max(max_current, current)
        else:
            current = 0
    max_streak = max(max_streak, max_current)

print(max_streak)