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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	private class Num implements Comparable<Num>{
		private int index = 0;
		private int num = 0;
		
		public Num(int index, int num) {
			this.index = index;
			this.num = num;
		}
		
		public boolean isEvenOrOdd(int evenOrOdd) {
			return (this.index % 2 == evenOrOdd);
		}

		@Override
		public int compareTo(Num o) {
			return Integer.compare(this.num, o.num);
		}
	}
	
	public long solve() {
		LinkedList<Num> list = new LinkedList<Num>();
		try (Scanner in = new Scanner(System.in)) {
			int N = in.nextInt();
			
			for (int i=0; i<N; i++) {
				list.addLast(new Num(i, in.nextInt()));
			}
		}
		list.sort(null);
		
		long count = 0;
		int index = 0;
		for (Num n : list) {
			if (n.isEvenOrOdd(index % 2) == false) {
				count++;
			}
			index++;
		}
		
		return count / 2;
	}
	
	public static void main(String[] args) {
		Main main = new Main();
		System.out.println(main.solve());
	}
}