Mountainous Palindromic Subarray

An array is *Mountainous* if it is strictly
increasing, then strictly decreasing. Note that
*Mountainous* arrays must therefore be of length three
or greater.

A *Subarray* is defined as an array that can be
attained by deleting some prefix and suffix (possibly empty)
from the original array.

An array or subarray is a *Palindrome* if it is the
same sequence forwards and backwards.

Given an array of integers, compute the length of the
longest *Subarray* that is both *Mountainous* and
a *Palindrome*.

The first line of input contains an integer $n$ ($1 \le n \le 10^6$), which is the number of integers in the array.

Each of the next $n$ lines contains a single integer $x$ ($1 \le x \le 10^9$). These values form the array. They are given in order.

Output a single integer, which is the length of the longest
*Mountainous Palindromic Subarray*, or $-1$ of no such array exists.

Sample Input 1 | Sample Output 1 |
---|---|

8 2 1 2 3 2 1 7 8 |
5 |

Sample Input 2 | Sample Output 2 |
---|---|

5 2 5 8 7 2 |
-1 |