from heapq import nlargest,heapify
def solve():
n=int(input());a=list(map(int,input().split()))
ind=a.index(max(a))
if a[:ind]==sorted(a[:ind]) and a[ind+1::]==sorted(a[ind+1::],reverse=True):print("YES")
else:print("NO")
solve()1546B - AquaMoon and Stolen String | 1353C - Board Moves |
902A - Visiting a Friend | 299B - Ksusha the Squirrel |
1647D - Madoka and the Best School in Russia | 1208A - XORinacci |
1539B - Love Song | 22B - Bargaining Table |
1490B - Balanced Remainders | 264A - Escape from Stones |
1506A - Strange Table | 456A - Laptops |
855B - Marvolo Gaunt's Ring | 1454A - Special Permutation |
1359A - Berland Poker | 459A - Pashmak and Garden |
1327B - Princesses and Princes | 1450F - The Struggling Contestant |
1399B - Gifts Fixing | 1138A - Sushi for Two |
982C - Cut 'em all | 931A - Friends Meeting |
1594A - Consecutive Sum Riddle | 1466A - Bovine Dilemma |
454A - Little Pony and Crystal Mine | 2A - Winner |
1622B - Berland Music | 1139B - Chocolates |
1371A - Magical Sticks | 1253A - Single Push |