How to uncomment several lines when some of these lines are not comments?

[gaoqiangks]

For example, I have three lines, the first and the third are comments, while the second is not.

# a=1
b=2
# c=3

When visually select these three lines and type gc, it will become

## a=1
#b=2
## c=3

I want it to become

a=1
b=2
c=3