You put in the whole thing
If your age was over 70.5, then there is a followup question on one of the pages that follows the main form, that lets you indicate how much went to the charity. But the $$ had to be directly transferred to the charity (with some exceptions). That will reduce the amount that is reported on line 4b of the form 1040
____________
If you were not over age 70.5 during 2019, then it is all taxable, but you enter the $$ you donated to the charity in the charity donations section.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
