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### Title

### 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 ≤ N ≤ 10`^{5}`1 ≤ A`_{i}≤ 10^{9}`A`is an integer._{i}

### Input

Input is given from Standard Input in the following format:

NA_{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 × 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

### Tags

### Subtasks and Limits

Subtask | Score | #TC | Time | Memory | Scoring |
---|---|---|---|---|---|

1 | 100 | 9 | 1s | 256MB | Minimum |

2 | 0 | 3 | 1s | 256MB | Minimum |

### Judge Compile Command

g++-8 ans.cpp -o makerectangle -Wall -Wshadow -static -O2 -lm -m64 -s -w -std=gnu++17 -fmax-errors=512