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)

from collections import Counter

n=int(input())
a=list(map(int,input().split()))

c=Counter(a)
l=c.most_common()
rectangle=[]
square=[]
x=len(l)
for i in range(x):
    if l[i][1]>=2:
        rectangle.append(l[i][0])
    if l[i][1]>=4:
        square.append(l[i][0])
rectangle.sort()
square.sort()
ans1=rectangle[-1]*rectangle[-2]
ans2=square[-1]**2
if ans1<ans2:
    print(ans2)
else:
    print(ans1)