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: Runtime Error)

import java.util.*;
import java.io.*;

public class Main {

    int[] a;
    int[] b;

    void solve() {
	int N = sc.nextInt();
	a = sc.nextIntArray(N);

	b = Arrays.copyOf(a, N);
	Arrays.sort(b);

	int[] c = new int[1000001];

	for (int i = 0; i < b.length; i++) {
	    c[b[i]] = i;
	}

	int ans = 0;
	for (int i = 0; i < a.length; i++) {
//	    System.out.println(c[a[i]]);
	    if (i % 2 == 0) {
		if (c[a[i]] % 2 != 0) {
		    ans++;
		}
	    }
	}
	System.out.println(ans);
    }

    void print(int[] a) {
	out.print(a[0]);
	for (int i = 1; i < a.length; i++) out.print(" " + a[i]);
	out.println();
    }

    public static void main(String[] args) throws Exception {
	new Main().run();
    }

    MyScanner sc = null;
    PrintWriter out = null;
    public void run() throws Exception {
	sc = new MyScanner(System.in);
	out = new PrintWriter(System.out);
	for (;sc.hasNext();) {
	    solve();
	    out.flush();
	}
	out.close();
    }

    class MyScanner {
	String line;
	BufferedReader reader;
	StringTokenizer tokenizer;

	public MyScanner(InputStream stream) {
	    reader = new BufferedReader(new InputStreamReader(stream));
	    tokenizer = null;
	}
	public void eat() {
	    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
		try {
		    line = reader.readLine();
		    if (line == null) {
			tokenizer = null;
			return;
		    }
		    tokenizer = new StringTokenizer(line);
		} catch (IOException e) {
		    throw new RuntimeException(e);
		}
	    }
	}
	public String next() {
	    eat();
	    return tokenizer.nextToken();
	}
	public String nextLine() {
	    try {
		return reader.readLine();
	    } catch (IOException e) {
		throw new RuntimeException(e);
	    }
	}
	public boolean hasNext() {
	    eat();
	    return (tokenizer != null && tokenizer.hasMoreElements());
	}
	public int nextInt() {
	    return Integer.parseInt(next());
	}
	public long nextLong() {
	    return Long.parseLong(next());
	}
	public double nextDouble() {
	    return Double.parseDouble(next());
	}
	public int[] nextIntArray(int n) {
	    int[] a = new int[n];
	    for (int i = 0; i < n; i++) a[i] = nextInt();
	    return a;
	}
    }
}