#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main() {
	int d;
	cin >> d;
	string c1, c8, c;
	cin >> c1 >> c8;
	c = c1 + c8;
	unsigned int weekday = 0x0;
	for (size_t i = 0; i < c.size(); ++i) {
		weekday <<= 1;
		weekday |= (c[i] == 'x');
	}
	int maxContinuousHolidays = 0;
	for (; d >= 0; --d) {
		unsigned int paid = (1 << d) - 1;
		for (size_t i = 0; i <= c.size() - d; ++i, paid <<= 1) {
			if ((weekday | paid) == weekday) {
				unsigned int newWeekday = weekday & ~paid;
				int continuousHolidays = 0;
				for (size_t k = 0; k < c.size(); ++k, newWeekday >>= 1) {
					if (newWeekday & 0x1) {
						maxContinuousHolidays = max(maxContinuousHolidays, continuousHolidays);
						continuousHolidays = 0;
					} else {
						++continuousHolidays;
					}
				}
				maxContinuousHolidays = max(maxContinuousHolidays, continuousHolidays);
			}
		}
	}
	cout << maxContinuousHolidays << endl;
	return 0;
}