The Computation / John Donne

FOR my first twenty years, since yesterday,
I scarce believed thou couldst be gone away ; 
For forty more I fed on favours past, 
And forty on hopes that thou wouldst they might last ; 
Tears drown'd one hundred, and sighs blew out two ;
A thousand, I did neither think nor do, 
Or not divide, all being one thought of you ;
Or in a thousand more, forgot that too.
Yet call not this long life ; but think that I
Am, by being dead, immortal ; can ghosts die ?