input: 
  def evaluate_postfix(expression: str) -> int:
      """Evaluate a postfix expression given as a string.
      >>> evaluate_postfix("2 3 + 4 5 * *")
      46
      >>> evaluate_postfix("10 4 3 + 2 * -")
      -4
      """
      tokens = expression.split()
      stack = []
      
      for token in tokens:
          if token.isdigit():
              stack.append(int(token))
          else:
              operand2 = stack.pop()
              operand1 = stack.pop()
              if token == '+':
                  stack.append(operand1 + operand2)
              elif token == '-':
                  stack.append(operand1 - operand2)
              elif token == '*':
                  stack.append(operand1 * operand2)
              elif token == '/':
                  stack.append(operand1 // operand2)
      
      return stack[0]
  
output:     tokens = expression.split()
      stack = []
      
      for token in tokens:
          if token.isdigit():
              stack.append(int(token))
          else:
              operand2 = stack.pop()
              operand1 = stack.pop()
              if token == '+':
                  stack.append(operand1 + operand2)
              elif token == '-':
                  stack.append(operand1 - operand2)
              elif token == '*':
                  stack.append(operand1 * operand2)
              elif token == '/':
                  stack.append(operand1 // operand2)
      
      return stack[0]