Problem:
Score : 700 points

Problem Statement

We have N cards numbered 1, 2, ..., N.
Card i (1 \leq i \leq N) has an integer A_i written in red ink on one side and an integer B_i written in blue ink on the other side.
Initially, these cards are arranged from left to right in the order from Card 1 to Card N, with the red numbers facing up.

Determine whether it is possible to have a non-decreasing sequence facing up from left to right (that is, for each i (1 \leq i \leq N - 1), the integer facing up on the (i+1)-th card from the left is not less than the integer facing up on the i-th card from the left) by repeating the operation below. If the answer is yes, find the minimum number of operations required to achieve it.

Choose an integer i (1 \leq i \leq N - 1).
Swap the i-th and (i+1)-th cards from the left, then flip these two cards.

Constraints

1 \leq N \leq 18

1 \leq A_i, B_i \leq 50 (1 \leq i \leq N)

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N
B_1 B_2 ... B_N

Output

If it is impossible to have a non-decreasing sequence, print -1.
If it is possible, print the minimum number of operations required to achieve it.

Sample Input 1

3
3 4 3
3 2 3

Sample Output 1

1

By doing the operation once with i = 1, we have a sequence [2, 3, 3] facing up, which is non-decreasing.

Sample Input 2

2
2 1
1 2

Sample Output 2

-1

After any number of operations, we have the sequence [2, 1] facing up, which is not non-decreasing.

Sample Input 3

4
1 2 3 4
5 6 7 8

Sample Output 3

0

No operation may be required.

Sample Input 4

5
28 15 22 43 31
20 22 43 33 32

Sample Output 4

-1

Sample Input 5

5
4 46 6 38 43
33 15 18 27 37

Sample Output 5

3

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.io.IOException;
import java.io.UncheckedIOException;
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
 */
public class Main {
    public static void main(String[] args) throws Exception {
        Thread thread = new Thread(null, new TaskAdapter(), "", 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);
            DSwapAndFlip solver = new DSwapAndFlip();
            solver.solve(1, in, out);
            out.close();
        }
    }

    static class DSwapAndFlip {
        public void solve(int testNumber, FastInput in, FastOutput out) {
            int n = in.readInt();
            int[] a = new int[n];
            int[] b = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = in.readInt();
            }
            for (int i = 0; i < n; i++) {
                b[i] = in.readInt();
            }
            int[] vals = new int[n];
            MultiWayIntegerDeque deque = new MultiWayIntegerDeque(51, n);
            int[] masks = new int[n];
            IntegerList perm = new IntegerList(n);
            int minCnt = (int) 1e8;

            for (int i = 0; i < (1 << n); i++) {
                boolean valid = true;
                for (int j = 0; j < n; j++) {
                    masks[j] = Bits.bitAt(i, j);
                    if (masks[j] == 1) {
                        vals[j] = b[j];
                    } else {
                        vals[j] = a[j];
                    }
                }
                for (int j = 0; j < n; j++) {
                    deque.addLast(vals[j], j);
                }
                int cnt = 0;
                for (int j = 0; j < n; j++) {
                    int p = 0;
                    for (int t = 0; t < n; t++) {
                        if (vals[t] > vals[j] && t < j ||
                                vals[t] < vals[j] && t > j) {
                            p++;
                        }
                    }
                    cnt += p;
                    masks[j] ^= p & 1;
                }
                cnt /= 2;

                for (int j = 1; j <= 50; j++) {
                    perm.clear();
                    while (!deque.isEmpty(j)) {
                        int last = deque.removeFirst(j);
                        perm.add(masks[last] ^ (perm.size() & 1));
                    }
                    if (perm.isEmpty()) {
                        continue;
                    }
                    int sum = 0;
                    int m = perm.size();
                    for (int k = 0; k < m; k++) {
                        sum += perm.get(k);
                    }
                    if (sum != perm.size() / 2) {
                        valid = false;
                    }
                    sum = 0;
                    for (int k = 0; k < m; k++) {
                        int val = perm.get(k);
                        if (val == 0) {
                            continue;
                        }
                        sum += val;
                        int target = sum * 2 - 1;
                        int dist = Math.abs(target - k);
                        cnt += dist;
                    }
                }

                if (!valid) {
                    continue;
                }
                minCnt = Math.min(minCnt, cnt);
            }

            if (minCnt == (int) 1e8) {
                out.println(-1);
            } else {
                out.println(minCnt);
            }
        }

    }

    static interface IntegerIterator {
        boolean hasNext();

        int next();

    }

    static class MultiWayIntegerDeque {
        private int[] values;
        private int[] next;
        private int[] prev;
        private int[] heads;
        private int[] tails;
        private int alloc;
        private int queueNum;

        public IntegerIterator iterator(final int queue) {
            return new IntegerIterator() {
                int ele = heads[queue];


                public boolean hasNext() {
                    return ele != 0;
                }


                public int next() {
                    int ans = values[ele];
                    ele = next[ele];
                    return ans;
                }
            };
        }

        private void doubleCapacity() {
            int newSize = Math.max(next.length + 10, next.length * 2);
            next = Arrays.copyOf(next, newSize);
            prev = Arrays.copyOf(prev, newSize);
            values = Arrays.copyOf(values, newSize);
        }

        public void alloc() {
            alloc++;
            if (alloc >= next.length) {
                doubleCapacity();
            }
            next[alloc] = 0;
        }

        public boolean isEmpty(int qId) {
            return heads[qId] == 0;
        }

        public MultiWayIntegerDeque(int qNum, int totalCapacity) {
            values = new int[totalCapacity + 1];
            next = new int[totalCapacity + 1];
            prev = new int[totalCapacity + 1];
            heads = new int[qNum];
            tails = new int[qNum];
            queueNum = qNum;
        }

        public void addLast(int qId, int x) {
            alloc();
            values[alloc] = x;

            if (heads[qId] == 0) {
                heads[qId] = tails[qId] = alloc;
                return;
            }
            next[tails[qId]] = alloc;
            prev[alloc] = tails[qId];
            tails[qId] = alloc;
        }

        public int removeFirst(int qId) {
            int ans = values[heads[qId]];
            if (heads[qId] == tails[qId]) {
                heads[qId] = tails[qId] = 0;
            } else {
                heads[qId] = next[heads[qId]];
                prev[tails[qId]] = 0;
            }
            return ans;
        }

        public String toString() {
            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < queueNum; i++) {
                builder.append(i).append(": ");
                for (IntegerIterator iterator = iterator(i); iterator.hasNext(); ) {
                    builder.append(iterator.next()).append(",");
                }
                if (builder.charAt(builder.length() - 1) == ',') {
                    builder.setLength(builder.length() - 1);
                }
                builder.append('\n');
            }
            return builder.toString();
        }

    }

    static class SequenceUtils {
        public static boolean equal(int[] a, int al, int ar, int[] b, int bl, int br) {
            if ((ar - al) != (br - bl)) {
                return false;
            }
            for (int i = al, j = bl; i <= ar; i++, j++) {
                if (a[i] != b[j]) {
                    return false;
                }
            }
            return true;
        }

    }

    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) {
                    bufLen = -1;
                }
                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;
        }

    }

    static class FastOutput implements AutoCloseable, Closeable {
        private StringBuilder cache = new StringBuilder(10 << 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);
            println();
            return this;
        }

        public FastOutput println() {
            cache.append(System.lineSeparator());
            return this;
        }

        public FastOutput flush() {
            try {
                os.append(cache);
                os.flush();
                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);
            }
        }

        public String toString() {
            return cache.toString();
        }

    }

    static class IntegerList implements Cloneable {
        private int size;
        private int cap;
        private int[] data;
        private static final int[] EMPTY = new int[0];

        public IntegerList(int cap) {
            this.cap = cap;
            if (cap == 0) {
                data = EMPTY;
            } else {
                data = new int[cap];
            }
        }

        public IntegerList(IntegerList list) {
            this.size = list.size;
            this.cap = list.cap;
            this.data = Arrays.copyOf(list.data, size);
        }

        public IntegerList() {
            this(0);
        }

        public void ensureSpace(int req) {
            if (req > cap) {
                while (cap < req) {
                    cap = Math.max(cap + 10, 2 * cap);
                }
                data = Arrays.copyOf(data, cap);
            }
        }

        private void checkRange(int i) {
            if (i < 0 || i >= size) {
                throw new ArrayIndexOutOfBoundsException("index " + i + " out of range");
            }
        }

        public int get(int i) {
            checkRange(i);
            return data[i];
        }

        public void add(int x) {
            ensureSpace(size + 1);
            data[size++] = x;
        }

        public void addAll(int[] x, int offset, int len) {
            ensureSpace(size + len);
            System.arraycopy(x, offset, data, size, len);
            size += len;
        }

        public void addAll(IntegerList list) {
            addAll(list.data, 0, list.size);
        }

        public int size() {
            return size;
        }

        public int[] toArray() {
            return Arrays.copyOf(data, size);
        }

        public boolean isEmpty() {
            return size == 0;
        }

        public void clear() {
            size = 0;
        }

        public String toString() {
            return Arrays.toString(toArray());
        }

        public boolean equals(Object obj) {
            if (!(obj instanceof IntegerList)) {
                return false;
            }
            IntegerList other = (IntegerList) obj;
            return SequenceUtils.equal(data, 0, size - 1, other.data, 0, other.size - 1);
        }

        public int hashCode() {
            int h = 1;
            for (int i = 0; i < size; i++) {
                h = h * 31 + Integer.hashCode(data[i]);
            }
            return h;
        }

        public IntegerList clone() {
            IntegerList ans = new IntegerList();
            ans.addAll(this);
            return ans;
        }

    }

    static class Bits {
        private Bits() {
        }

        public static int bitAt(int x, int i) {
            return (x >> i) & 1;
        }

    }
}