题目描述

Ziv has $n$ pairs of sticks, numbered from 1 to $n$. The $i$-th pair consists of two sticks, each of length $a[i]$.

Ziv intends to construct a rectangular frame by selecting two distinct indices $x$ and $y$ ($x \ne y$). The resulting rectangle will have side lengths $a[x]$ by $a[y]$, and an area equal to $a[x] \times a[y]$.

Help Ziv find the maximum possible area of a rectangular frame he can construct.

输入格式

Your program must read from standard input.

The first line of input contains one integer $n$.

The next $n$ lines of input each contain one integer. The $i$-th of these lines contains $a[i]$.

输出格式

Your program must print to standard output.

Output one integer, the maximum possible area of a rectangular frame Ziv can form.

The output should contain only a single integer. Do not print any additional text such as Enter a number or The answer is.

2
8
9

72

3
16
44
18

792

8
6
7
6
7
99
99
69
1

9801

提示

Sample Test Case 1 Explanation

Only one frame is possible: $8 \times 9$ with an area of $72$.

Sample Test Case 2 Explanation

There are only 3 frames possible:

• $16 \times 44 = 704$
• $16 \times 18 = 288$
• $44 \times 18 = 792$

The largest area is $792$.

Subtasks

For all test cases, the input will satisfy the following bounds:

• $2 \le n \le 10$
• $1 \le a[i] \le 1000$ for all $1 \le i \le n$

Your program will be tested on input instances that satisfy the following restrictions:

Subtask	Score	Additional Constraints
0		Sample test cases
1	20	$n = 2$
2		$n = 3$
3	60	No additional constraints