#include <iostream>
#include <vector>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)

int main(void){
	int n; cin >> n;
	string s1, s2; cin >> s1 >> s2;
	string s = "xxxxxxxxxxxxxx" + s1 + s2 + "xxxxxxxxxxxxxx";
	int ans = 0, tmp = 0;
	for (int i = 0; i < 42 - n; ++i){
		tmp = 0;
		string t = s;
		for (int j = i; j < i + n; ++j){
			t[j] = 'o';
		}
		// cout << t << endl;
		rep(j, t.size()){
			// printf("%d\n", tmp);
			if(t[j] == 'o') tmp++;
			else{
			// printf("i %d\n", i);
				ans = max(tmp, ans);
				tmp = 0;
			}
			if(j == t.size() - 1) ans = max(tmp, ans);
		}
	}
	cout << ans << endl;
	return 0;
}