Mountain Array Verification

You are given an array of integers. An array is considered a mountain array if and only if:

• The array has at least 3 elements.
• There exists an index \( i \) with \( 1 \leq i \leq n-2 \) such that:
• The sequence \( a_0, a_1, \dots, a_i \) is strictly increasing.
• The sequence \( a_i, a_{i+1}, \dots, a_{n-1} \) is strictly decreasing.

Your task is to read an array from the standard input and determine whether the array is a mountain array. Print YES if it is, or NO otherwise.

Note: The input is provided from stdin and the result should be printed to stdout.

inputFormat

The input consists of two lines:

• The first line contains a single integer \( n \) ( \( n \geq 1 \)), representing the number of elements in the array.
• The second line contains \( n \) space-separated integers \( a_0, a_1, \dots, a_{n-1} \) representing the elements of the array.

outputFormat

Print a single line to stdout:

• YES if the array is a mountain array.
• NO otherwise.

2
2 1

NO