Problem:
Score : 300 points

Problem Statement

We have N sticks with negligible thickness.
The length of the i-th stick is A_i.

Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides.
Find the maximum possible area of the rectangle.

Constraints

4 \leq N \leq 10^5

1 \leq A_i \leq 10^9

A_i is an integer.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible area of the rectangle.
If no rectangle can be formed, print 0.

Sample Input 1

6
3 1 2 4 2 1

Sample Output 1

2

1 \times 2 rectangle can be formed.

Sample Input 2

4
1 2 3 4

Sample Output 2

0

No rectangle can be formed.

Sample Input 3

10
3 3 3 3 4 4 4 5 5 5

Sample Output 3

20

Solution in Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;


public class Main {


	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String in = sc.nextLine();
		int count = Integer.parseInt(in);
		String inLine = sc.nextLine();
		String[] inArray = inLine.split(" ");
		int[] intArray1 = new int[count];
		int[] intArray2 = new int[count];

		List<Integer> lines = new ArrayList<Integer>();
		for (int i = 0; i < count; i++) {
			intArray1[i] = Integer.parseInt(inArray[i]);
		}
		intArray2 = intArray1.clone();
		for (int i = 0 ; i < count; i++) {
			for (int j = 0; j < count;j++) {
				if (intArray1[i] == intArray2[j] && i != j) {
					Integer n1 = new Integer(intArray1[i]);
					if (!lines.contains(n1)) {
						lines.add(n1);
					}
					break;
				}
			}
		}
		if (lines.size() < 1){
			System.out.println(0);
		} else {
			Collections.sort(lines);
			if (lines.size() == 1) {
				int n1 = lines.get(lines.size()-1).intValue();
				System.out.println(n1 * n1);
			} else {
				int n1 = lines.get(lines.size()-1).intValue();
				int n2 = lines.get(lines.size()-2).intValue();
				System.out.println(n1 * n2);
			}
		}

	}


}