# N,M,K=map(int, input().split())
# D=[[] for i in range(N)]
# for i in range(M):
#   a,b,d=map(int, input().split())
#   a-=1;b-=1
#   D[a].append((d,b));D[b].append((d,a))

N=int(input())
A=list(map(int, input().split()))

D={}
B=[-100]
for i in range(N):
  a=A[i]
  if i>=1 and B[-1]==a:
    continue
  B.append(a)
B.append(-100)

if max(B)>N:
  print('No')
  exit()
  
from collections import deque
d=deque()
D={}
f=0 
for i in range(1,len(B)-1):
  if B[i-1]<B[i] and B[i]>B[i+1]:
    b=B[i]
    if b not in D:
      D[b]=[]
    D[b].append(i)
    
    
V=[0]*len(B)
V[0]=1;V[-1]=1
for i in range(max(B),1,-1):  
  if i in D:
    for nex in D[i]:
      d.append(nex)
  nd=deque()
  while d:
    ff=0 
    now=d.popleft()
    if B[now-1]+1==B[now]:
      ff=1 
      if V[now-1]==0:
        V[now-1]=1
        nd.append(now-1)
    if B[now+1]+1==B[now]:
      ff=1 
      if V[now+1]==0:
        V[now+1]=1
        nd.append(now+1)
  if ff==0:
    print('No')
    exit()    
  else:
    d=nd 
print('Yes')