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())
L = list(map(int,input().split()))
P = list(set(L))
if len(P) == len(L) :
    ans = 0
else :
    D = {}
    ans = 1
    for i in range(N) :
        if L[i] not in D :
            D[L[i]] = 1
        else :
            D[L[i]] += 1
    D = sorted(D.items(),key=lambda x: x[0], reverse=True)
    flag = 0
    for i in range(len(D)) :
        if D[i][1] >= 4 and flag < 1 :
            ans *= D[i][0]**2
            flag += 2
        elif D[i][1] >= 2 and flag < 2 :
            ans *= D[i][0]
            flag += 1
print(ans)