Someone has let a goat in a square kitchen-garden and had bound it to a stake. The stake is driven into the ground in the very midst of the square. The goat is hungry as a hunter and very voracious, and eats everything that can be reached without leaving the square and tearing off the rope. What area of the kitchen-garden will be ate round?

Input

  Contains lengths of the garden sides and a cord length in meters (positive integers not exceeding 1000, located in one line and separated with a space).

Output               

   Should contain an area of the kitchen-garden (in square meters to within 6 symbols after a decimal point), ate round by the goat.

Samples