input: def evaluate_postfix(expression: str) -> int:
      """
      Evaluate a postfix expression given as a string and return the result as an integer.
      >>> evaluate_postfix("2 3 + 4 5 * *")
      46
      """
      # split expression into list
      tokens = expression.split()
      
      # stack to store integer values.
      stack = []
      
      # iterate through each token in the expression
      for token in tokens:
          if token.isdigit():
              # If the token is a digit, push it onto the stack
              stack.append(int(token))
          else:
              # If the token is an operator, pop two elements from the stack
              operand2 = stack.pop()
              operand1 = stack.pop()
              
              # Perform the operation and push the result back onto the stack
              if token == '+':
                  stack.append(operand1 + operand2)
              elif token == '-':
                  stack.append(operand1 - operand2)
              elif token == '*':
                  stack.append(operand1 * operand2)
              elif token == '/':
                  stack.append(operand1 // operand2)  # Use integer division for postfix expressions
      
      # The result should be the only element in the stack
      return stack[0]
output:     # The result should be the only element in the stack
      return stack[0]