IRD calculation

I inherited a traditional IRA from my mom.
Her estate was over the lifetime exemption by $49680., which resulted in a tax bill of $19872.
AS I take money out of the IRA I should be able to deduct the withdrawals out until I have a tax savings equal to the taxes paid on the estate. But since I am not taking it all at once, I know I need to do it over time.
My question is how do I figure out what number to use for "estate deduction not shown on a K1".

Taxed inheritance 49,680. inheritance tax paid $19872.

The value of the IRA at death was $395,849. I took $30,000 last year.
Do I use:
(49,680/395,849)*30,000 =3765.07
or
(19872/395849)*30,000= 1629.52
The first one allows me to deduct the amount of income that was already taxed while the second one only allows me to deduct the tax that was paid.
Which calculation should I use?