text: """
  {x | x in (-10, 10)}
  {x^2 | x in (0, 5)}
  
  (f(var) for variable in iterable)
  """
  
  # g = [i ** 2 for i in range(1, 11)]
  # print(type(g))
  # print(g)
  
  # print([character for character in input()])
  
  # print(max([1, 2, 3, 4, 5]))
  # print(min([1, 2, 3, 4, 5]))
  # print(sum([i for i in range(1, 11)]))
  
  n = int(input())
  print(sum(i for i in range(1, n + 1)))
  