The brave Knight came to the King and asked permission to marry the princess. The King knew that the Knight was brave, but he also wanted to know if he was smart enough. So he asked him to solve the following task.

There is a permutation p_i of numbers from 1 to 2n. You can make two types of operations. 

  1. Swap p_1 and p_2, p_3 and p_4, ..., p_{2n-1} and p_{2n}. 
  2. Swap p_1 and p_{n+1}, p_2 and p_{n+2}, ..., p_{n} and p_{2n}. 



The task is to find the minimal number of operations required to sort the given permutation.

The Knight was not that smart actually, but quite charming, so the princess asks you to help him to solve the King's task.

Input

The first line contains the integer n (1≤ n≤ 1000). The second line contains 2n integers p_i — the permutation of numbers from 1 to 2n.

Output

Print one integer — the minimal number of operations required to sort the permutation. If it is impossible to sort the permutation using these operations, print -1.

Examples

Input


3
6 3 2 5 4 1


Output


3


Input


2
3 4 2 1


Output


-1


Input


4
1 2 3 4 5 6 7 8


Output


0

Note

In the first example, you can sort the permutation in three operations: 

  1. Make operation 1: 3, 6, 5, 2, 1, 4. 
  2. Make operation 2: 2, 1, 4, 3, 6, 5. 
  3. Make operation 1: 1, 2, 3, 4, 5, 6. 
//package Codeforces.ICPC_EurasiaFinals2021;

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

public class K {
    static boolean isPerfect(int[] arr){
        for(int i=0;i<arr.length-1;i++){
            if(arr[i]>arr[i+1])
                return false;
        }
        return true;
    }
    static void ops1(int[] arr){
        for(int i=0;i<arr.length;i+=2){
            int t = arr[i];
            arr[i] = arr[i+1];
            arr[i+1] = t;
        }
    }
    static void ops2(int[] arr){
        for(int i=0;i<arr.length/2;i++){
            int t = arr[i];
            arr[i] = arr[arr.length/2+i];
            arr[arr.length/2+i] = t;
        }
    }
    static int check1(int[] arr){
        int n = arr.length/2;
        int[] a = new int[2*n];
        System.arraycopy(arr, 0, a, 0, 2*n);

        int limit;
        if(n%2==0){
            limit = 4;
        }
        else{
            limit = 2*n;
        }

        for(int i=0;i<limit;i++){
            if(isPerfect(a))
                return i;

            if(i%2==0){
                ops1(a);
            }
            else{
                ops2(a);
            }
        }

        return -1;
    }
    static int check2(int[] arr){
        int n = arr.length/2;
        int[] a = new int[2*n];
        System.arraycopy(arr, 0, a, 0, 2*n);

        int limit;
        if(n%2==0){
            limit = 4;
        }
        else{
            limit = 2*n;
        }

        for(int i=0;i<limit;i++){
            if(isPerfect(a))
                return i;

            if(i%2==0){
                ops2(a);
            }
            else{
                ops1(a);
            }
        }

        return -1;
    }
    public static void main(String[] args) throws IOException {
        Soumit sc = new Soumit();

        int n = sc.nextInt();
        int[] arr = sc.nextIntArray(2*n);

        int c1 = check1(arr);
        int c2 = check2(arr);

        if(c1==-1 && c2==-1){
            System.out.println(-1);
        }
        else if(c1==-1){
            System.out.println(c2);
        }
        else if(c2==-1){
            System.out.println(c1);
        }
        else{
            System.out.println(Math.min(c1, c2));
        }

        sc.close();
    }

    static class Soumit {
        final private int BUFFER_SIZE = 1 << 18;
        final private DataInputStream din;
        final private byte[] buffer;
        private PrintWriter pw;
        private int bufferPointer, bytesRead;
        StringTokenizer st;

        public Soumit() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Soumit(String file_name) throws IOException {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public void streamOutput(String file) throws IOException {
            FileWriter fw = new FileWriter(file);
            BufferedWriter bw = new BufferedWriter(fw);
            pw = new PrintWriter(bw);
        }

        public void println(String a) {
            pw.println(a);
        }

        public void print(String a) {
            pw.print(a);
        }

        public String readLine() throws IOException {
            byte[] buf = new byte[3000064]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1) {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

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

        public void sort(int[] arr) {
            ArrayList<Integer> arlist = new ArrayList<>();
            for (int i : arr)
                arlist.add(i);

            Collections.sort(arlist);
            for (int i = 0; i < arr.length; i++)
                arr[i] = arlist.get(i);
        }

        public void sort(long[] arr) {
            ArrayList<Long> arlist = new ArrayList<>();
            for (long i : arr)
                arlist.add(i);

            Collections.sort(arlist);
            for (int i = 0; i < arr.length; i++)
                arr[i] = arlist.get(i);
        }

        public int[] nextIntArray(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }

            return arr;
        }

        public long[] nextLongArray(int n) throws IOException {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }

            return arr;
        }

        public double[] nextDoubleArray(int n) throws IOException {
            double[] arr = new double[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextDouble();
            }

            return arr;
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException {
            /*if (din == null)
                return;*/
            if (din != null) din.close();
            if (pw != null) pw.close();
        }
    }
}
