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. 
"""
    Author - Satwik Tiwari .

"""

#===============================================================================================
#importing some useful libraries.

from __future__ import division, print_function
from fractions import Fraction
import sys
import os
from io import BytesIO, IOBase
from functools import cmp_to_key

# from itertools import *
from heapq import *
from math import gcd, factorial,floor,ceil,sqrt,log2

from copy import deepcopy
from collections import deque


from bisect import bisect_left as bl
from bisect import bisect_right as br
from bisect import bisect

#==============================================================================================
#fast I/O region
BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


def print(*args, **kwargs):
    """Prints the values to a stream, or to sys.stdout by default."""
    sep, file = kwargs.pop("sep", " "), kwargs.pop("file", sys.stdout)
    at_start = True
    for x in args:
        if not at_start:
            file.write(sep)
        file.write(str(x))
        at_start = False
    file.write(kwargs.pop("end", "\n"))
    if kwargs.pop("flush", False):
        file.flush()


if sys.version_info[0] < 3:
    sys.stdin, sys.stdout = FastIO(sys.stdin), FastIO(sys.stdout)
else:
    sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)

# inp = lambda: sys.stdin.readline().rstrip("\r\n")

#===============================================================================================
### START ITERATE RECURSION ###
from types import GeneratorType
def iterative(f, stack=[]):
  def wrapped_func(*args, **kwargs):
    if stack: return f(*args, **kwargs)
    to = f(*args, **kwargs)
    while True:
      if type(to) is GeneratorType:
        stack.append(to)
        to = next(to)
        continue
      stack.pop()
      if not stack: break
      to = stack[-1].send(to)
    return to
  return wrapped_func
#### END ITERATE RECURSION ####

#===============================================================================================
#some shortcuts

def inp(): return sys.stdin.readline().rstrip("\r\n") #for fast input
def out(var): sys.stdout.write(str(var))  #for fast output, always take string
def lis(): return list(map(int, inp().split()))
def stringlis(): return list(map(str, inp().split()))
def sep(): return map(int, inp().split())
def strsep(): return map(str, inp().split())
# def graph(vertex): return [[] for i in range(0,vertex+1)]
def testcase(t):
    for pp in range(t):
        solve(pp)
def google(p):
    print('Case #'+str(p)+': ',end='')
def lcm(a,b): return (a*b)//gcd(a,b)
def modInverse(b):
    g = gcd(b, mod)
    if (g != 1):
        # print("Inverse doesn't exist")
        return -1
    else:
        # If b and m are relatively prime,
        # then modulo inverse is b^(m-2) mode m
        return pow(b, mod - 2, mod)
def power(x, y, p) :
    y%=(p-1)  #not so sure about this. used when y>p-1. if p is prime.
    res = 1     # Initialize result
    x = x % p  # Update x if it is more , than or equal to p
    if (x == 0) :
        return 0
    while (y > 0) :
        if ((y & 1) == 1) : # If y is odd, multiply, x with result
            res = (res * x) % p

        y = y >> 1      # y = y/2
        x = (x * x) % p
    return res
def isPrime(n) :
    if (n <= 1) : return False
    if (n <= 3) : return True
    if (n % 2 == 0 or n % 3 == 0) : return False
    i = 5
    while(i * i <= n) :
        if (n % i == 0 or n % (i + 2) == 0) :
            return False
        i = i + 6
    return True
inf = pow(10,20)
mod = 10**9+7
#===============================================================================================
# code here ;))

def op1(a,pos):
    n = len(a)//2
    for i in range(n):
        if(pos == 2*i):
            newpos = 2*i+1
        elif(pos == 2*i+1):
            newpos = 2*i
        a[2*i],a[2*i+1] = a[2*i+1],a[2*i]

    return a,newpos

def op2(a,pos):
    n = len(a)//2
    for i in range(n):
        if(pos == i):
            newpos = i+n
        elif(pos == i+n):
            newpos = i
        a[i],a[i+n] = a[i+n],a[i]

    return a,newpos

def solve(case):
    n = int(inp())
    a = lis()
    n*=2
    ans = 0
    for i in range(1):
        # print(a)
        pos = -1
        for j in range(n):
            if(a[j] == i+1):
                pos = j
        correctpos = i

        if(pos == correctpos):
            if(a == sorted(a)):
                print(0)
            else:
                print(-1)
            return

        new = deepcopy(a)
        f = False
        cnt = 0
        for j in range(n):
            if(j%2):
                new,pos = op1(new,pos)
            else:
                new,pos = op2(new,pos)
            cnt += 1
            if(pos == correctpos):
                f = True
                break

        pos = -1
        for j in range(n):
            if (a[j] == i + 1):
                pos = j

        new2 = deepcopy(a)
        cnt2 = 0
        for j in range(n):
            if (j % 2):
                new2, pos = op2(new2, pos)
            else:
                new2, pos = op1(new2, pos)
            cnt2 += 1
            if (pos == correctpos):
                f = True
                break

        if(f):
            if(cnt < cnt2):
                if(new == sorted(new)):
                    print(cnt)
                else:
                    if(new2 == sorted(new2)):
                        print(cnt2)
                    else:
                        print(-1)
            else:
                if(new2 == sorted(new2)):
                    print(cnt2)
                else:
                    if(new == sorted(new)):
                        print(cnt)
                    else:
                        print(-1)
        else:
            print(-1)




testcase(1)
# testcase(int(inp()))





