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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define ld long double
#define pii pair <int, int>
#define sz(a) (int)(a.size()) 
#define resize(v) v.resize(unique(all(v)) - v.begin()); 
#define all(a) a.begin(), a.end()
#define forit(it, s) for(__typeof(s.begin()) it = s.begin(); it != s.end(); it ++)

using namespace std;
 
void Fast_Read_Out()
{
    ios_base::sync_with_stdio(0);
    cin.tie(), cout.tie();
}
 
void Random()
{
    unsigned int seed;                                                                        
    asm("rdtsc" : "=A" (seed));
    srand(seed);        
}
 
unsigned int Time()
{
     unsigned int time = clock() / 1000.00;                           
     return time;
}
 
const int mod = (int)1e9 + 7;
const int N = int(1e5) + 123;

int a[N];
 
int main ()
{
	#ifdef JUDGE
		freopen("input.txt", "r", stdin);
	#endif		
	Fast_Read_Out();
	Random();
	int n;
	cin >> n;
	int ans = 0;
	for(int i = 1; i <= n; i++) cin >> a[i];
	for(int i = 1; i < n; i++) if(a[i] > a[i + 1]) ans++;
	cout << ans % 2 << endl;
}