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: Runtime Error)

def findsq(a,b,c,d):
    if a == b and c == d:
        return 1
    elif a == c and b == d:
        return 1
    elif a == d and b == c:
        return 1
    else: 
        return 0

if __name__ == '__main__':
    N = int(input())
    A = map(int, input().split())
    ans = 0
    for i in range(N-3):
        for j in range(i, N-2):
            for k in range(j, N-1):
                for l in range(k, N):
                    if findsq(A[i], A[j], A[k], A[l]) == 1:
                        ans += 1
    print(ans)