Title
Problem Statement
We have N sticks with negligible thickness.
The length of the i-th stick is Ai.
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 ≤ N ≤ 105
- 1 ≤ Ai ≤ 109
- Ai is an integer.
Input
Input is given from Standard Input in the following format:
N
A1 A2 ... AN
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 × 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