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().rstrip()
second_week = input().rstrip()
golden_weeks = 'x' * 14 + first_week + second_week + 'x' * 14
longest = longest_holidays(golden_weeks)
for d in range(1, D + 1):
    for i in range(42 - d + 1):
        if golden_weeks[i:i+d] == 'x' * d:
            weeks = golden_weeks[:i] + 'o' * d + golden_weeks[i + d:]
            longest = max(longest_holidays(weeks), longest)
print(longest)