The first of a month is put into A1

What formula can I put into C1, E1, G1, etc (ie alternate columns) which will give me the first of the following month?

I cannot put =A1+31 because the month in A1 is not necessarily a 31 day month and there might be a leap year.

(I am wanting to set up a calendar which is automatically set from whatever month is set in A1)