n_ew = input('RUN and STOP : ')
if n_ew == 'RUN':
    r_un = True
else:
    print 'Game over'
while r_un:
    i = raw_input('number: ')
    if i == 'quit':
         break
    else:
        k = input ('k = ')
        for j in range(k):
                print j
    continue
print 'Game over'

用PYcharm测试时一直报：

RUN and STOP : RUN
Traceback (most recent call last):
  File "C:/Users/Administrator/Desktop/2.2.py", line 1, in <module>
    n_ew = input('RUN and STOP : ')
  File "<string>", line 1, in <module>
NameError: name 'RUN' is not defined

该如何定义 RUN

非常感谢，问题已经解决。
输入字符串必须使用：raw_input()

n_ew = raw_input('RUN and STOP : ')