keep row that contains certain string pandas

Question

I have this dataframe

id           value
high           3
medium         2
low            1
NaN
service
complex
high           5
medium         4
low            3

and what I want to do is to keep the row that contains high, medium, low only. So I expect my dataframe would become:

id           value
high           3
medium         2
low            1
high           5
medium         4
low            3

what I have tried is using str.contains

df[df['id'].str.contains('high', 'medium', 'low')]

but it gives me error TypeError: unsupported operand type(s) for &: 'str' and 'int'

how can I do that with pandas?

thanks in advance