a=0
for i in range(a):
	b=int(input())
	c=list(map(int,input().split()))
	xyz=[0,0,0]
	if c[0]<c[1]:
		print('No')
		continue
	for j in range(b):
		if c[j]>c[j+1]:
			xyz[0]=j
			break
	if xyz[0]==0:
	    print('No')
	    continue
	for j in range(xyz[0],b):
		if c[j]>c[j+1]:
			xyz[1]=j
			break
	if xyz[1]==0:
		print('No')
		continue
	for j in range(xyz[1],b):
		if c[j]<c[j+1]:
			xyz[2]=j
			break
	if xyz[2]==0:
		print('No')
		continue
	for j in range(xyz[2],b):
		if c[j]>c[j+1]:
			xyz[2]=0
	if xyz[2]==0:
		print('No')
		continue
	print('Yes')