Suppose that a country has no public debt in year 1 butexperiences a budget deficit of

$ 40$40

billion in year? 2, a budget surplus of

$ 10$10

billion in year? 3, a budget surplus of

$ 15$15

billion in year? 4, and a budget deficit of

$ 4$4

billion in year 5.

The absolute size of public debt at the end of year 5 is

?$nothing

billion. ?(Enter your response as a whole? number.)