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 PyPy3 (2.4.0) (judge verdict: Accepted)

import collections
N=int(input())
A=list(map(int,input().split()))
l=[]
c=collections.Counter(A)
a=[]
values=list(c.values())
key=list(c.keys())
b=[]
for i in range(len(key)):
    l.append([key[i],values[i]])
l.sort(key=lambda x:x[1],reverse=True)
for i in range(len(l)):
    if l[i][1]>=2:
        num=l[i][0]
        b=[num]*((l[i][1])//2)
        a.extend(b)
if len(a)<2:
    print("0")
else:
    a.sort(reverse=True)
    print(a[0]*a[1])