import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.util.Random;
import java.util.ArrayList;
import java.io.UncheckedIOException;
import java.util.List;
import java.io.Closeable;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.InputStream;

/**
 * Built using CHelper plug-in Actual solution is at the top
 * 
 * @author daltao
 */
public class Main {
    public static void main(String[] args) throws Exception {
        Thread thread = new Thread(null, new TaskAdapter(), "daltao", 1 << 27);
        thread.start();
        thread.join();
    }

    static class TaskAdapter implements Runnable {
        @Override
        public void run() {
            InputStream inputStream = System.in;
            OutputStream outputStream = System.out;
            FastInput in = new FastInput(inputStream);
            FastOutput out = new FastOutput(outputStream);
            TaskF solver = new TaskF();
            solver.solve(1, in, out);
            out.close();
        }
    }
    static class TaskF {
        public void solve(int testNumber, FastInput in, FastOutput out) {
            int n = in.readInt();
            char[] s = new char[n + 1];
            char[] t = new char[n + 1];
            in.readString(s, 1);
            in.readString(t, 1);

            List<Interval> intervalList = new ArrayList<>(n);
            int scan = n + 1;
            for (int i = n; i >= 1; i--) {
                if (scan > i) {
                    scan = i;
                }
                if (s[scan] == t[i]) {
                    continue;
                }
                while (s[scan] != t[i] && scan > 1) {
                    scan--;
                }
                if (s[scan] != t[i]) {
                    out.println(-1);
                    return;
                }
                Interval interval = new Interval();
                interval.l = scan;
                interval.r = i;
                intervalList.add(interval);
            }

            Interval[] intervals = intervalList.toArray(new Interval[0]);
            ArrayUtils.reverse(intervals, 0, intervals.length);

            int m = intervals.length;
            int[] perm = new int[m];
            for (int i = 0; i < m; i++) {
                perm[i] = i;
            }
            Randomized.randomizedArray(perm, 0, m);

            int ans = 0;
            for (int i = 0; i < m; i++) {
                int j = perm[i];
                if (j + ans >= m || intervals[j].r <= intervals[j + ans].l - (ans)) {
                    continue;
                }
                int l = ans + 1;
                int r = m - j;
                while (l < r) {
                    int mid = (l + r) >> 1;
                    if (j + mid >= m || intervals[j].r <= intervals[j + mid].l - mid) {
                        r = mid;
                    } else {
                        l = mid + 1;
                    }
                }
                ans = l;
            }

            out.println(ans);
        }

    }
    static class FastOutput implements AutoCloseable, Closeable {
        private StringBuilder cache = new StringBuilder(1 << 20);
        private final Writer os;

        public FastOutput(Writer os) {
            this.os = os;
        }

        public FastOutput(OutputStream os) {
            this(new OutputStreamWriter(os));
        }

        public FastOutput println(int c) {
            cache.append(c).append('\n');
            return this;
        }

        public FastOutput flush() {
            try {
                os.append(cache);
                cache.setLength(0);
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
            return this;
        }

        public void close() {
            flush();
            try {
                os.close();
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }

    }
    static class ArrayUtils {
        public static <T> void swap(T[] data, int i, int j) {
            T tmp = data[i];
            data[i] = data[j];
            data[j] = tmp;
        }

        public static <T> void reverse(T[] data, int f, int t) {
            int l = f, r = t - 1;
            while (l < r) {
                swap(data, l, r);
                l++;
                r--;
            }
        }

    }
    static class Randomized {
        static Random random = new Random();

        public static void randomizedArray(int[] data, int from, int to) {
            to--;
            for (int i = from; i <= to; i++) {
                int s = nextInt(i, to);
                int tmp = data[i];
                data[i] = data[s];
                data[s] = tmp;
            }
        }

        public static int nextInt(int l, int r) {
            return random.nextInt(r - l + 1) + l;
        }

    }
    static class FastInput {
        private final InputStream is;
        private byte[] buf = new byte[1 << 13];
        private int bufLen;
        private int bufOffset;
        private int next;

        public FastInput(InputStream is) {
            this.is = is;
        }

        private int read() {
            while (bufLen == bufOffset) {
                bufOffset = 0;
                try {
                    bufLen = is.read(buf);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
                if (bufLen == -1) {
                    return -1;
                }
            }
            return buf[bufOffset++];
        }

        public void skipBlank() {
            while (next >= 0 && next <= 32) {
                next = read();
            }
        }

        public int readInt() {
            int sign = 1;

            skipBlank();
            if (next == '+' || next == '-') {
                sign = next == '+' ? 1 : -1;
                next = read();
            }

            int val = 0;
            if (sign == 1) {
                while (next >= '0' && next <= '9') {
                    val = val * 10 + next - '0';
                    next = read();
                }
            } else {
                while (next >= '0' && next <= '9') {
                    val = val * 10 - next + '0';
                    next = read();
                }
            }

            return val;
        }

        public int readString(char[] data, int offset) {
            skipBlank();

            int originalOffset = offset;
            while (next > 32) {
                data[offset++] = (char) next;
                next = read();
            }

            return offset - originalOffset;
        }

    }
    static class Interval {
        int l;
        int r;

    }
}



Measured memory_bytes: 87892