'''
   You have to use the following template to submit to Revel.
   Note: To test the code using the CheckExerciseTool, you will submit entire code.
   To submit your code to Revel, you must only submit the code enclosed between
     # BEGIN REVEL SUBMISSION

     # END REVEL SUBMISSION
'''

class Stack:
    def __init__(self):
        self.__elements = []

    # Return true if the stack is empty
    def isEmpty(self):
        return len(self.__elements) == 0
    
    # Returns the element at the top of the stack 
    # without removing it from the stack.
    def peek(self):
        if self.isEmpty():
            return None
        else:
            return self.__elements[len(self.__elements) - 1]

    # Stores an element into the top of the stack
    def push(self, value):
        self.__elements.append(value)

    # Removes the element at the top of the stack and returns it
    def pop(self):
        if self.isEmpty():
            return None
        else:
            return self.__elements.pop() 
    
    # Return the size of the stack
    def getSize(self):
        return len(self.__elements)

def main():
    expression = input("Enter an expression: ").strip()
    try:
        print(expression, "=", evaluateExpression(expression))
    except:
        print("Wrong expression: ", expression)

# BEGIN REVEL SUBMISSION

# Evaluate an expression 

# Write Your Code Here

# END REVEL SUBMISSION