是一道加减乘的表达式计算的题目，easy
```
import Queue
def chengfa(cs):
stack = Queue.LifoQueue()
begin = 0
for i in range(len(cs)):
if cs[i] == "*" :
stack.put(cs[begin:i])
begin=i+1
stack.put(cs[begin:])
result = int(stack.get())
while not stack.empty():
result *= int(stack.get())
return result
while True:
s = raw_input()
if s == "END" :
break
else :
num = Queue.Queue()
operator = Queue.Queue()
begin=0
for i in range(len(s)):
if s[i] == "+" or s[i] == "-":
num.put(chengfa(s[begin:i]))
begin = i + 1
operator.put(s[i])
num.put(chengfa(s[begin:]))
result = num.get()
while not num.empty():
if operator.get() == "+":
result += num.get()
else:
result -= num.get()
print result
```