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

#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define repp(i,n) for(int (i)=1;(i)<=(n);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define clr(a) memset((a), 0 ,sizeof(a))


typedef pair<int,int> P;
typedef vector<pair<int,string> > pii;
typedef map<string,int> mi;



int main(){
	int n,i,M=-1,sum,cnt;
	bool ok;
	string s,s2;
	cin >> n >> s >> s2;
	s="xxxxxxxxxxxxxx"+s+s2+"xxxxxxxxxxxxxx";
	
	for(i=0;i<s.size();i++){
		s2=s;
		ok=false;
		sum=0;
		cnt=n;
		if(s2[i]=='x'){
			for(int j=i;j<s2.size();j++){
				if(s2[j]=='o'||cnt==0)break;
				s2[j]='o';
				cnt--;
			}
		}
		else{
			for(int j=i;j<s2.size();j++){
				if((s2[j]=='o'&&ok)||cnt==0)break;
				if(s2[j]=='x'){
					ok=true;
					s2[j]='o';
					cnt--;
				}
			}
		}
		
		for(int j=i;j<s2.size();j++){
			if(s2[j]=='x')break;
			sum++;
		}
		M=max(M,sum);
	}
	cout << M << endl;
	return 0;
}