The following list represents CPM network of a project.

Activity Normal time $($day$)$ Crash time $($days$)$

Normal cost

Crash cost Predecessor

A $86$ $$1,000$ $$1,600---$

B $107$ $$2,000$ $$2,600---$

C $54$ $$500$ $$1,000$ A

D $97$ $$4,000$ $$4,200$ A$,$ B

E $21$ $$3,000$ $$4,000$ C$,$ D

Suppose that the project manager is willing to spend any amount of cost to complete the project as fast as possible. What will be the project duration after the crashing $($i$.$e$.,$ crashing to the maximum extent without concerning the crashing cost$)?$