Statement

Given a triangle with sides of length $a$, $b$, and $c$, its area is $\sqrt{p(p-a)(p-b)(p-c)}$, where $p=\frac{1}{2}(a+b+c)$. Input these three numbers and calculate the area of the triangle, rounded to $1$ decimal place. If the three sides cannot form a triangle, output No

Input

Input three real numbers $a, b, c$ on the first line, separated by spaces.

Output

Output a real number representing the area of the triangle, accurate to $1$ decimal place. If it cannot be formed, output No.

Samples

3 4 5

6.0

3 14 5

No

Notes

$0\leq a,b,c\leq 1000$, and each edge length is input with no more than $2$ decimal places.