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

int main() {
	int holiday;
	std::string weeks, s;

	std::cin >> holiday;
	std::cin >> s;
	weeks = s;
	std::cin >> s;
	weeks += s;

	int max = 0;
	for (int i = 0; i < weeks.length(); i++) {
		int count = 0, holi_num = 0;
		for (int j = i; j < weeks.length(); j++) {
			if (weeks[j] == 'x') {
				if (count == holiday) {
					break;
				}
				count++;
			}
			holi_num++;
		}
		holi_num += holiday - count;
		max = std::max(max, holi_num);
	}

	std::cout << max << std::endl;
	return 0;
}