import java.io.File;
import java.util.*;

public class Main {
	static int cul(String a){
		int ans=0;
		for(int i=0;i<a.length();i++){
			if(a.charAt(i)=='o'){
				int temp=1;
				int j=1;
				while(i+j<a.length() && a.charAt(i+j)=='o'){
					j++;
					temp++;
				}
				ans=Math.max(ans, temp);
				i+=j;
			}
		}
		return ans;
	}
	public static void main(String[] args){
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		String a = sc.next();
		String b = sc.next();
		a+=b;
		int ans=0;
		String aa ="xxxxxxxxxxxxxxxxxxxxxxxx";
		aa+=a;
		aa+="xxxxxxxxxxxxxxxxxxxx";
		for(int k=0;k<=n;k++){
		String rep ="";
		for(int w=0;w<k;w++) rep+="o";
		//System.out.println(rep);
		int i=0;
		tt:while(i+k-1<aa.length()){
			for(int j=i;j<i+k;j++){
				if(aa.charAt(j)=='o'){
					i++;
					continue tt;
				}
			}
			StringBuilder c = new StringBuilder(aa);
			c.replace(i, i+k,rep);
			//System.out.println(c);
			ans=Math.max(ans, cul(c.toString()));
			i++;
		}
		}
		System.out.println(ans);
	}
}