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: Wrong Answer)

n = int(input())
a = sorted(list(map(int,input().split())))[::-1]
a += [0, 0, 0]

l1, l2 = 0, 0
ind = -1

for i in range(n):
  if a[i] == a[i+3] and l1 != 0:
    print(a[i]*a[i])
    exit()
  elif a[i] == a[i+1] and ind != i-1: 
    if l1 == 0:
      l1 = a[i]
      ind = i
    else:
      l2 = a[i]
      print(l1 * l2)
      exit()

print(0)