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

d={}


for i in range(n):
    if a[i] in d:
        d[a[i]]+=1
    else:
        d[a[i]]=1

can = list(d.items())

edge=[]
for i in range(len(can)):
    if can[i][1]<2:
        continue
    else:
        edge.append(can[i])

if len(edge)==0:
    print(0)
    exit(0)
elif len(edge)==1 and edge[0][1]<4:
    print(0)
    exit(0)
elif len(edge)==1 and edge[0][1]>=4:
    print(edge[0][0]**2)
    exit(0)

edge = sorted(edge,key=lambda x: x[0],reverse=True)

k=len(edge)

s=1
if edge[0][1]>=4:
    print(edge[0][0]**2)
else:
    print(edge[0][0]*edge[1][0])