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: import numpy as np
  
  N = input().split()
  
  Nsum = list()
  op = list()
  for i in range(len(N) - 1):
      if N[i].isdigit():
          op.append(float(N[i]))
      else:
          if N[i] == "+":
              Nsum.append(op[0] + op[1])
              op = list()
          elif N[i] == "-":
              Nsum.append(op[0] - op[1])
              op = list()
          elif N[i] == "*":
              Nsum.append(op[0] * op[1])
              op = list()
  
  
  if N[-1] == "+":
      print(np.sum(Nsum))
  elif N[-1] == "-":
      Nsub = Nsum[0]
      for n in Nsum[1:]:
          Nsub -= n
      print(Nsub)
  
  elif N[-1] == "*":
      print(np.prod(Nsum))
  
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"}]