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 (2.7.6) (judge verdict: Accepted)

n = int(raw_input())
d = map(int, raw_input().split())
dict = {}
for i in range(n):
    if dict.has_key(d[i]):
        dict[d[i]] += 1
    else:
        dict[d[i]] = 1
dict = sorted(dict.items())
ans = []
for i in range(len(dict)-1, -1, -1):
    if dict[i][1] > 3:
        if len(ans) == 0:
            ans = [dict[i][0], dict[i][0]]
            break
        else:
            ans.append(dict[i][0])
            break
    elif dict[i][1] > 1:
        if len(ans) > 0:
            ans.append(dict[i][0])
            break
        else:
            ans.append(dict[i][0])
if len(ans) > 1:
    print ans[0]*ans[1]
else:
    print 0