#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
using namespace std;

int main(){
	int d;
	cin >> d;
	string a,b;
	cin >> a >> b;

	string c = "xxxxxxx";

	string s = c+c;
	s += a;
	s += b;
	s += c+c;

	vector<int> begin;
	vector<int> end;
	int last = -100;
	int tmp = 0;
	for(int i=0; i<s.size(); i++){
		if(s[i] == 'o'){
			if(last == i-1){

			}else{
				begin.push_back(i);

			}
			last = i;
		}else if(last == i-1){
			end.push_back(i-1);
		}
	}

	int ans = 0;
	if(begin.size() == 0){
		ans = d;
	}else{
		ans = end[0] - begin[0] + 1 + d;
	}

	for(int i=0; i<begin.size(); i++){
		if(i+1 < begin.size() && begin[i+1] - end[i] - 1 <= d){
			ans = max(ans, end[i+1] - begin[i] + 1);
		}else{
			ans = max(ans, end[i] - begin[i] + 1 + d);
		}
	}

	cout << ans << endl;

	return 0;
}