#E A, B, C = gets.chomp.split.map(&:to_i)
N = gets.chomp.to_i
H = gets.chomp.split.map(&:to_i)

def can_decrease?
  1.upto(N - 1).each do |i|
    if H[i] < H[i-1]
      return false
    elsif H[i] == H[i-1]
      # continue
    else  # H[i] > H[i-1]
      H[i] -= 1
      # continue
    end
  end
  
  true
end

r = can_decrease?

# p H
if r
  print "Yes\n"
else
  print "No\n"
end