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: Accepted)

n = int(input())
a = list(map(int,input().split()))
aset = set()
a2set = set()
a3set = set()
a4set = set()
for i in a:
    if i in a3set:
        a4set.add(i)
    if i in a2set:
        a3set.add(i)
    if i in aset:
        a2set.add(i)
    aset.add(i)
if len(a2set) < 2 and len(a4set) == 0:
    ans = 0
else:
    x = max(a2set)
    if x in a4set:
        ans = x ** 2
    else:
        a2set.remove(x)
        y = max(a2set)
        ans = x * y
print(ans)