Triangle Area Calculation

Given three integers representing the sides of a triangle, determine whether they can form a valid triangle. If they can, compute the area of the triangle using Heron's formula. Otherwise, output -1.

Heron's formula is given by:
[ A = \sqrt{s (s-A)(s-B)(s-C)}] where (s = \frac{A+B+C}{2}) is the semi-perimeter of the triangle.

inputFormat

The input consists of a single line containing three space-separated integers, (A), (B), and (C), representing the lengths of the sides of a triangle.

outputFormat

Output the area of the triangle as a floating-point number if the three sides can form a valid triangle using the triangle inequality; otherwise, output -1.## sample

3 4 5

6