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## C. Goat in the Garden

Time limit: 1.0 second
Memory limit: 64 MB
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 100, located in one line and separated with a space).

### Output

should contain an area of the kitchen-garden (in square meters to within 3 symbols after a decimal point), ate round by the goat.

### Sample

inputoutput
10 6
95.091
Problem Author: Irina Danilina
Problem Source: The 3rd high school children programming contest, USU, Yekaterinburg, Russia, March 4, 2001
To submit the solution for this problem go to the Problem set: 1084. Goat in the Garden