Thousand wants to drink a cup of tea.

The volume of his teacup is 1 unit and it is empty initially. Thousand will not drink the tea unless the teacup is full.

Thousand places the teacup on his table, and waits for his assistant BSP to fill the teacup.

Every time BSP visits Thousand's office, BSP will bring a pot with  units of tea randomly, and fill them all into Thousand's teacup.

Thousand wants to know the expected number of visits his assistant has to make so that he can drink the tea.

Note that  and  are real numbers.