Triangle Area via Heron's Formula

You are given three positive numbers representing the sides of a triangle. Your task is to calculate the area of the triangle using Heron's formula.

The area A is calculated as:

$$A = \sqrt{s(s-a)(s-b)(s-c)}$$

where the semi-perimeter s is defined as:

$$s = \frac{a+b+c}{2}$$

You can assume that the given sides always form a valid triangle.

inputFormat

The input consists of a single line containing three space-separated positive numbers a, b and c which denote the lengths of the sides of the triangle.

outputFormat

Output the area of the triangle. The answer should be printed rounded to three decimal places.

sample

3 4 5

6.000