A. Unimodal Array
time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

Array of integers is unimodal, if:

  • it is strictly increasing in the beginning;
  • after that it is constant;
  • after that it is strictly decreasing.

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.

Input

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 ≤ 1 000) — the elements of the array.

Output

Print "YES" if the given array is unimodal. Otherwise, print "NO".

You can output each letter in any case (upper or lower).

Examples
Input
6
1 5 5 5 4 2
Output
YES
Input
5
10 20 30 20 10
Output
YES
Input
4
1 2 1 2
Output
NO
Input
7
3 3 3 3 3 3 3
Output
YES
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#include <vector>
#include <cstdlib>
#include <iomanip>
#include <cmath>
#include <ctime>
#include <map>
#include <set>
using namespace std;
#define lowbit(x) (x&(-x))
#define max(x,y) (x>y?x:y)
#define min(x,y) (x<y?x:y)
#define MAX 100000000000000000
#define MOD 1000000007
#define pi acos(-1.0)
#define ei exp(1)
#define PI 3.141592653589793238462
#define INF 0x3f3f3f3f3f
#define mem(a) (memset(a,0,sizeof(a)))
typedef long long ll;
int main()
{
int a[],n,x;
scanf("%d",&n);
for(int i=;i<=n;i++)
{
scanf("%d",&a[i]);
}
int l=,r=n;
while(l<n && a[l]<a[l+]) l++;
while(r> && a[r]<a[r-]) r--;
for(int i=l+;i<=r;i++)
if(a[i]!=a[l]) return puts("NO"),;
puts("YES");
return ;
}

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