def longest_holidays(weeks):
    longest = 0
    x = 0
    for day in weeks:
        if day == 'o':
            x += 1
            if x > longest:
                longest = x
        else:
            x = 0
    return longest

d = int(input())
first_week = input()
second_week = input()
golden_weeks = first_week + second_week
longest = 0
for i in range(14):
    for j in range(i+1, min(i + d, 14) + 1):
        if 'o' not in golden_weeks[i:j]:
            weeks = golden_weeks[:i] + 'o' * (j - i) + golden_weeks[j:]
            longest = max(longest_holidays(weeks), longest)
print(longest)