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 (3.8.2) (judge verdict: Accepted)

# -*- coding: utf-8 -*-
import sys
from collections import deque, defaultdict
from math import sqrt, factorial, gcd
# def input(): return sys.stdin.readline()[:-1] # warning not \n
# def input(): return sys.stdin.buffer.readline().strip() # warning bytes
# def input(): return sys.stdin.buffer.readline().decode('utf-8')


def solve():
    n = int(input())
    a = [int(x) for x in input().split()]
    d = defaultdict(int)
    for e in a:
        d[e] += 1
    sq = []
    re = []
    for k in d:
        if d[k] > 1:
            re.append(k)
        if d[k] > 3:
            sq.append(k)
    sq.sort()
    re.sort()
    ans = 0
    if sq:
        ans = sq[-1] * sq[-1]
    if len(re) > 1:
        ans = max(ans, re[-1] * re[-2])
    print(ans)

        



t = 1
# t = int(input())
for case in range(1,t+1):
    ans = solve()


"""



"""