output_description: Print the computational result in a line.
input_description: An expression is given in a line. Two consequtive symbols (operand or
  operator) are separated by a space character.
  
  You can assume that +, - and * are given as the operator and an operand is a
  positive integer less than 106
attempt: formula_str = input()
  formula_splitted = formula_str.split()
  
  
  def initialize(List):
      List[0] = 0
  
  
  def IsEmpty(List):
      List[0] == 0
  
  
  def IsFull(List):
      List[0] >= len(List) - 1
  
  
  def push(List, val):
      if IsFull == True:
          raise ValueError("Full")
      List[0] += 1
      List[List[0]] = val
  
  
  def pop(List):
      if IsEmpty == True:
          raise ValueError("Empty")
      content = List[List[0]]
      List[0] -= 1
      return content
  
  
  formula = [0 for i in range(0, len(formula_splitted) + 1)]
  for content in formula_splitted:
      if content == "*":
          val1, val2 = pop(formula), pop(formula)
          push(formula, val2 * val1)
      elif content == "+":
          val1, val2 = pop(formula), pop(formula)
          push(formula, val2 + val1)
      elif content == "-":
          val1, val2 = pop(formula), pop(formula)
          push(formula, val2 - val1)
      else:
          push(formula, int(content))
  
  print(pop(formula))
  
problem_description: Input
  
  An expression is given in a line. Two consequtive symbols (operand or
  operator) are separated by a space character.
  
  You can assume that +, - and * are given as the operator and an operand is a
  positive integer less than 106
samples: [{"input": "1 2 +", "output": "3"}, {"input": "1 2 + 3 4 - *", "output": "-3"}]