//package timus;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.StringTokenizer;

public class p1423 {
    static char[] t;
    static char[] p;
    static int[] pi;
    static int N;

    public static void main(String[] args) throws FileNotFoundException {
        InputStream is = System.in;
        FastScanner sc = new FastScanner(new InputStreamReader(is));
        N = sc.nextInt();
        String tt = sc.next();
        tt += tt;
        t = tt.toCharArray();
        p = sc.next().toCharArray();
        pi = new int[N];
        System.out.println(KMPMatcher());
    }

    static int KMPMatcher() {
        computePrefixFunction();
        int equals = 0;
        for (int i = 0; i < N + N; i++) {
            while (equals > 0 && p[equals] != t[i])
                equals = pi[equals - 1];
            if (p[equals] == t[i])
                equals++;
            if (equals == N) {
                if (i == N - 1) {
                    return 0;
                } else {
                    return N + N - (i + 1);
                }
            }
        }
        return -1;
    }

    static void computePrefixFunction() {
        int k = 0;
        for (int q = 1; q < N; q++) {
            while (k > 0 && p[k] != p[q])
                k = pi[k - 1];
            if (p[k] == p[q])
                k++;
            pi[q] = k;
        }
    }

    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        FastScanner(Reader in) {
            br = new BufferedReader(in);
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }
    }
}