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: Wrong Answer)

#ARc081C

n=int(raw_input())
l=map(int,raw_input().split())
l1=list(set(l))
l2=[]
l4=[]
for i in xrange(len(l1)):
 if 2<=l.count(l1[i])<4:
  l2.append(l1[i])
 elif l.count(l1[i])>=4:
  l4.append(l1[i])
res=0
if len(l4)==0 and len(l2)<=1:
 res=0
elif len(l4)==0:
 res=l2[-1]*l2[-2]
elif len(l4) and len(l2)==0:
 res=l4[-1]*l4[-1]
elif len(l4) and len(l2)==1:
 res=l4[-1]*l2[-1]
else:
 res=max(l4[-1]*l4[-1],l4[-1]*l2[-1],l2[-1]*l2[-2])
print res