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 Python (3.4.3) (judge verdict: Runtime Error)

def solve(): # 071C - Make a Rectangle
    n = int(input())
    sides = list(map(int, input().split(" ")))
    check_dual = {}
    possible_sides = []

    for i in sides:
        if i in check_dual:
            check_dual[i] += 1
        else:
            check_dual[i] = 1

    tmp_square = 0
    for k, v in check_dual.items():
        if v >= 4 and k > tmp_square:
            tmp_square = k
        elif v == 2 or v == 3:
            possible_sides.append(k)
        else:
            pass

    possible_sides.sort(reverse=True)
    if tmp_square == 0 and len(possible_sides) < 2:
        print(0)
    else:
        print(max(possible_sides[0] * possible_sides[1],
                  tmp_square ** 2))


solve()