#include "bits/stdc++.h"
using namespace std;

int main() {
	int D;
	cin >> D;
	string s1, s2;
	cin >> s1 >> s2;
	s1 += s2;
	int ans = D;

	int cnt2 = 0;
	s1 = "xxxxxxxxxxxxxxxxxxxx" + s1 + "xxxxxxxxxxxxxxxxxxxxxx";

	for (int i = 0; i < s1.size(); i++)
	{
		if (s1[i] == 'o'){
			cnt2++;
			ans = max(cnt2, ans);
		}
		else cnt2 = 0;
	}

	if (D == 0){
		cout << ans << endl;
		return 0;
	}

	for (int j = 0; j < s1.size(); j++)
	{
		int tempans = 0;
		int cnt = 0;
		tempans = cnt;
		int j2 = j;
		for (int i = 0; i < s1.size(); i++)
		{
			if (((i - j2) >= 0 && (i - j2) < D)){
				if (s1[i] == 'o'){
					//tempans = -10000;
					//break;
					cnt++;
					tempans = max(tempans, cnt);
					j2 = -10000;
				}
				else{
					cnt++;
					tempans = max(tempans, cnt);
				}
			}
			else if (s1[i] == 'o'){
				cnt++;
				tempans = max(tempans, cnt);
			}
			else cnt = 0;
			

			/*
			if ((((i - j) >= 0 && (i - j) < D)) || s1[i] == 'o'){
				cnt++;
				tempans = max(tempans, cnt);
			}
			else cnt = 0;
			*/
		}
		if (tempans < 0) continue;
		tempans = max(cnt, tempans);
		ans = max(ans, tempans);
	}
	//ans = min(ans, 14);
	cout << ans << endl;
	cin >> ans;
}