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())
A=[int(i) for i in input().split()]
A.sort()
cnt={}
K=list(set(A))
K.sort()
for k in K:
  cnt[k]=0
for a in A:
  cnt[a]+=1
E=[]
for k in K:
  if cnt[k]>=2:
    if cnt[k]>4:
      E.append(k)
    E.append(k)
E.sort()
# print(E)
if len(E)>=2:
  print(E[-1]*E[-2])
else:
  print(0)