Enclosure

Pahom walks around as large an area as he wants, starting at daybreak and
ending at sunset, using his spade to make markers as he goes. The polygon
marked out by his markers as vertices represents the land Pahom has claimed.

Pahom walks at a speed of one metre per second, each marker cost  seconds to
make, the total available time between daybreak and sunset is  seconds. Find
the maximum area Pahom could claim.

Pahom must return to the starting point by the end.

Input
  The first line of input contains the number of cases,  ().

  The next  line of input each consist of two space-separated integers  and 
  () - the time required to make one marker, and the total time
  available to Pahom.

Output
  For each case, output a real number representing the maximum area.
  
  Your answers should have an absolute or relative error of at most .