n = gets.to_i
h = gets.split.map &:to_i
(n-1).downto(0) do |i|
  if i == 0
    puts "Yes"
    exit
  end
  if h[i-1] - h[i] > 1
    puts "No"
    exit
  elsif h[i-1] - h[i] == 1
    h[i-1] -= 1
  end
end
