I need a formula that can calculate the following:

If month($B$2) equal month (D10) the maximum it can calculate to is 1,
otherwise add D11+D12-D13
The formula is in D14. So one month that correspond with B2 is going to
have a value of 1 or less when you add row 11and 12 then minus13. while the
other will have the right result.