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 C++ (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
using namespace std;
struct number_{
	int n;
	int index;
}seq[100002];
int comp1(number_ a,number_ b){
	return a.n<b.n;
}
int comp2(number_ a,number_ b){
	return a.index<b.index;
}
int n,ans=0;
int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>seq[i].n;
		seq[i].index=i;
	}
	sort(seq,seq+n,comp1);
	for(int i=0;i<n;i++){
		seq[i].n=i%2;
	}
	sort(seq,seq+n,comp2);
	for(int i=0;i<n;i+=2){
		ans+=seq[i].n;
	}
	cout<<ans<<endl;
	return 0;
}