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

int main(void){
	string s1,s2;
	int d;
	cin >> d;
	cin >> s1 >> s2;
	s1 += s2;

	int ret = 0;
	for(int i=0;i<(1<<14);i++){
		int a=0;
		if(__builtin_popcount(i) > d)continue;
		for(int j=0;j<14;j++){
			if(s1[j] == 'o' || (1<<j)&i)a++;
			else a=0;
			ret = max(a,ret);
		}
	}
	cout << ret << endl;
	return 0;
}