#include <iostream>
#include <string>
#include <map>
#include <cmath>
#include <algorithm>
#include <vector>

using namespace std;

int ret = 0;
void dfs(int n,int d,string& s1,int renkyu){
	if(n == 14){
		ret = max(ret,renkyu);
		return;
	}
	ret = max(ret,renkyu);
	if(s1[n] == 'o')dfs(n+1,d,s1,renkyu+1);
	else{
		if(d>0)dfs(n+1,d-1,s1,renkyu+1);
		dfs(n+1,d,s1,0);
	}
	return;
}

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

	dfs(0,n,s1,0);
	cout <<ret << endl;

	return 0;
}