Array of integers is unimodal, if:
The first block (increasing) and the last block (decreasing) may be absent. It is allowed that both of this blocks are absent.
For example, the following three arrays are unimodal: [5,7,11,11,2,1], [4,4,2], [7], but the following three are not unimodal: [5,5,6,6,1], [1,2,1,2], [4,5,5,6].
Write a program that checks if an array is unimodal.
The first line contains integer n (1≤n≤100) − the number of elements in the array.
The second line contains n integers a1,a2,...,an (1≤ai≤1000) − the elements of the array.
Print "YES" if the given array is unimodal. Otherwise, print "NO".
You can output each letter in any case (upper or lower).
6
1 5 5 5 4 2
YES
5
10 20 30 20 10
YES
4
1 2 1 2
NO
7
3 3 3 3 3 3 3
YES
In the first example the array is unimodal, because it is strictly increasing in the beginning (from position 1 to position 2, inclusively), that it is constant (from position 2 to position 4, inclusively) and then it is strictly decreasing (from position 4 to position 6, inclusively).