A special quadrilateral is inscribed in a circle. The speciality about this quadrilateral is that one of its diagonals is the diameter of the circle. Look at the image for better understanding.

You are given the length of radius of the circle and any two opposote sides of the quadrilateral, i.e either AB&CD or BC&AD

Output the area of the quadrilateral correct upto two decimal digits.

Input Format

• The first and only lines contain three integers the length of radius R and the opposite sides of the quadrilateral A  and B

Output Format

• Print the area of the quadrilateral with exactly 2 decimal places.

Note: Print exactly 2 decimal places or else you will get wrong answer verdict.

Also, scan the numbers as INTEGERS and not floating points and use DOUBLE for calculations and output as this can lead to precision errors.

Constraints

$1 \le A,B \lt 2*R \le 10000$