#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int c(string w) {
	int d = 0, ret = 0;
	for(int i = 0; i < 42; i++) {
		if(w[i] == 'o') d++;
		else d = 0;
		ret = max(ret, d);
	}
	return ret;
}

int main() {
	int d;
	string w, w1, w2;
	cin >> d >> w1 >> w2;
	w = "xxxxxxxxxxxxxx" + w1 + w2 + "xxxxxxxxxxxxxx";

	int ans = 0;
	for(int i = 0; i <= 28; i++) {
		string ww = w;
		bool flag = true;
		for(int j = 0; j < d; j++) {
			if(ww[i + j] == 'o') {
				flag = false;
				break;
			}
			ww[i + j] = 'o';
		}
		if(flag) {
			ans = max(ans, c(ww));
		}
	}

	cout << ans << endl;
}