import java.util.*;
import java.io.*;
import static java.util.Arrays.*;
import static java.lang.Math.*;

public class No0204 {
    
    static final Scanner in = new Scanner(System.in);
    static final PrintWriter out = new PrintWriter(System.out,false);

    static void solve() {
        int d = in.nextInt();
        String s = in.next();
        String t = in.next();
        String x = "xxxxxxxxxxxxxx";
        s = x + s + t + x;
        char[] cs = s.toCharArray();


        int res = 0;
        for (int i=0; i<cs.length; i++) {
            char[] clone = cs.clone();

            for (int j=i; j-i<d && j<cs.length; j++) {
                if (j < cs.length-1 && clone[j] == 'x' && clone[j+1] == 'o') {
                    clone[j] = 'o';
                    break;
                }
                clone[j] = 'o';
            }

            res = max(res,count(clone));
        }

        out.println(res);
    }

    static int count(char[] cs) {
        int res = 0;
        for (int i=1; i<cs.length; i++) {
            if (cs[i] == 'x') continue;
            int cnt = 1;
            while (i < cs.length && cs[i] == cs[i-1]) {
                cnt++;
                i++;
            }
            res = max(res,cnt);
        }

        return res;
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();

        solve();
        out.flush();

        long end = System.currentTimeMillis();
        //trace(end-start + "ms");
        in.close();
        out.close();
    }

    static void trace(Object... o) { System.out.println(deepToString(o));}
}