n = gets.chomp.to_i
input = gets.chomp.split(' ').map(&:to_i)
ans = ''
if n == 1
  ans = 'Yes'
elsif n > 1
  (0..n-1).each_cons(2) do |a, b|
    diff = input[b] - (input[a] + 1)
    if diff >= 0
      ans = 'Yes'
    else
      ans = 'No'
    end
  end
end
puts ans
