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: allst = list(input().split())
  stk = []
  ans = 0
  for i in range(0, len(allst)):
      if allst[i] == "+":
          stk[len(stk) - 2] = stk[len(stk) - 2] + stk[len(stk) - 1]
          del stk[len(stk) - 1]
      elif allst[i] == "-":
          stk[len(stk) - 2] = stk[len(stk) - 2] - stk[len(stk) - 1]
          del stk[len(stk) - 1]
      elif allst[i] == "*":
          stk[len(stk) - 2] = stk[len(stk) - 2] * stk[len(stk) - 1]
          del stk[len(stk) - 1]
      else:
          stk.append(int(allst[i]))
  print(stk[len(stk) - 1])
  
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"}]