Problem:
Score : 600 points

Problem Statement

Snuke got an integer sequence of length N from his mother, as a birthday present. The i-th (1 ≦ i ≦ N) element of the sequence is a_i. The elements are pairwise distinct.
He is sorting this sequence in increasing order.
With supernatural power, he can perform the following two operations on the sequence in any order:

Operation 1: choose 2 consecutive elements, then reverse the order of those elements.

Operation 2: choose 3 consecutive elements, then reverse the order of those elements.

Snuke likes Operation 2, but not Operation 1. Find the minimum number of Operation 1 that he has to perform in order to sort the sequence in increasing order.

Constraints

1 ≦ N ≦ 10^5

0 ≦ A_i ≦ 10^9

If i ≠ j, then A_i ≠ A_j.

All input values are integers.

Input

The input is given from Standard Input in the following format:

N
A_1
:
A_N

Output

Print the minimum number of times Operation 1 that Snuke has to perform.

Sample Input 1

4
2
4
3
1

Sample Output 1

1

The given sequence can be sorted as follows:

First, reverse the order of the last three elements. The sequence is now: 2,1,3,4.

Then, reverse the order of the first two elements. The sequence is now: 1,2,3,4.

In this sequence of operations, Operation 1 is performed once. It is not possible to sort the sequence with less number of Operation 1, thus the answer is 1.

Sample Input 2

5
10
8
5
3
2

Sample Output 2

0

Solution in Ruby (2.3.3) (judge verdict: Accepted)


N=gets.to_i
A=Array.new(N)
N.times do |i|
  A[i]=[gets.to_i,i]
end
A.sort!
samecount=[0,0]

ans=0
N.times do |i|
  samecount[A[i][1]%2]+=1
  if i==N-1 || A[i][0]!=A[i+1][0]
    startm1=i-samecount[0]-samecount[1]
    if startm1==-1
      evennum=i/2+1
    else
      evennum=i/2-startm1/2
    end
    ans+=(samecount[0]-evennum).abs
    samecount=[0,0]
  end
end

p ans/2