gets.to_i
numbers = gets.split.map(&:to_i)

result = "Yes"
(numbers.size-1).downto(1) do |i|
  # theory numbers[i] > numbers[i-1]
  numbers[i-1] -= 1 if numbers[i] < numbers[i-1]
  result = "No" if numbers[i] < numbers[i-1]
end

puts result