Area of a triangle

Given the length of three segments. Construct a triangle where one of these segments would be the height, one - the bisector and one - the median of triangle. All segments must go out from the same vertex.

Input

Three positive doubles - the lengths of segments (the length of each segment ranges from 0.01 to 100).

Output

Print one number - the area of constructed triangle with accuracy 0.001. If its not possible to construct triangle, print -1. If several triangles can be constructed with different areas, print 0.

Examples