Description

Input the three edges of an random triangle,Calculate the area of the triangle and output it. p=$\frac{a+b+c}{2}$
x=$p\times(p-a)\times(p-b)\times(p-c)$
s=$\sqrt x$

Input Format

Three integers in a row.

Output Format

One number.

5 6 6

14.697

Limit and hint

For $100\%$ testcases， $a,b,c\leq10^5$.