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 解():
    iN = int(input())
    aA = [int(_) for _ in input().split()]
    aA = reversed(sorted(aA))
    d = {}
    for a in aA:
        if a in d:
            if d[a] == 3:
                print(a*a)
                exit()
            elif iC and iC != a:
                print(iC * a)
                exit()
            else:
                iC = a
                d[a] += 1
        else:
            d[a] = 1
    print(0)
解()