def solve():
  N = int(input())
  A = list(map(int, input().split()))
  if N==1:
    return 'Yes'
  end = N-1
  for i in range(N-1,0,-1):
    if A[i]!=0:
      end = i
      break
    if i==1 and A[i]==0:
      return 'Yes'
  for i in range(1,end):
    if A[i]!=i:
      return 'No'
  if A[end]!=end+1:
    return 'No'
  return 'Yes'
print(solve())