import java.util.*;
import java.lang.*;
import java.io.*;

class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		double a, b, alpha, h=0;
		Scanner sc = new Scanner(System.in);
		a = sc.nextDouble();
		b = sc.nextDouble();
		alpha = sc.nextDouble();
		h = ((a-b) / 2 ) * Math.tan(alpha);
		System.out.format("%f", h * ( (a+b) / 2));
	}
}