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)

from collections import Counter
N, *a = map(int, open(0).read().split())

c = Counter(a).most_common()
c = sorted([[i, j // 2] for i, j in c], reverse=True)
ans = 1
cnt = 0
for i in range(len(c)):
    a, v = c[i]
    while v > 0:
        ans *= a
        cnt += 1
        v -= 1
        if cnt == 2:
            break
    if cnt == 2:
      break
            
print(ans if cnt == 2 else 0)