What is the inverse of the sentence, "If Sam leaves, then I will stay."?

The logical inverse of an if-then statement p -> q is

~p -> ~q

For us 

p is "if Sam leaves" so ~p is "If Sam does not leave"

and q is "I will stay" so ~q is "I will not stay"

Therefore the inverse is:

If Sam does not leave, then I will not stay.