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 Pascal (FPC 3.0.4) (judge verdict: Runtime Error)

program taska;
var n, a, i, temp, cnt : longint;
    p : array[1..1000] of longint;
begin
    readln(n);
    for i := 1 to n do
    begin
        readln(a);
        p[i] := a;
    end;
    
    for i := 1 to n do
    begin
        if p[i] > p[i + 2] then
        begin
            temp := p[i];
            p[i] := p[i + 2];
            p[i + 2] := temp;
        end
        else 
        begin
            temp := p[i];
            p[i] := p[i + 1];
            p[i + 1] := temp;
            inc(cnt);   
        end;
    end;
    writeln(cnt);
end.