import math
import string

variables = {}

def resolve(argument):
    if argument[0] in string.letters:
        if variables.has_key(argument):
            return variables[argument]
        else:
            print 'Unknown variable:', argument
            return 0.0
    else:
        return float(argument)

operations = {}

def add(a,b,last):
    last = resolve(a) + resolve(b)
    print last
    return last
operations['+'] = add

def subtract(a,b,last):
    last = resolve(a) - resolve(b)
    print last
    return last
operations['-'] = subtract

def multiply(a,b,last):
    last = resolve(a) * resolve(b)
    print last
    return last
operations['*'] = multiply

def store(a,b,last):
    variables[a] = last
    print a, '=', last
    return last
operations['store'] = store

def clear(a,b,last):
    variables.clear()
    print 'Variables cleared.'
    return last
operations['clear'] = clear


doLoop = True
last = 0.0
while doLoop:
    userInput = raw_input('? ').split(' ')
    if userInput[0] == 'exit':
        doLoop = False
    else:
        if operations.has_key(userInput[0]):
            if len(userInput) == 3:
                args = userInput[1:3]+[last]
            elif len(userInput) == 2:
                args = userInput[1:2]+[None, last]
            else:
                args = [None, None, last]
            result = apply(operations[userInput[0]],args)
        else:
            print 'Unknown operation.'