import java.text.DecimalFormat;
import java.util.Scanner;

public class Q {
	public static double equationSolver(double A, double B){
		double r = 10000000000.0;
		while (compute(r, B) < A){
			r *= 2;
		}

		double low = B / (2 * Math.PI);
		double high = r;
		double mid = r/2;
		while (Math.abs(compute(mid, B) - A) >= Math.pow(10, -25)){
			if (compute(mid, B) - A >= 0){
				high = mid;
			}
			else {
				low = mid;
			}
			mid = (high + low) / 2;
		}
		
		return mid;
	}
	
	public static double compute(double r, double B){
		return 2 * r * Math.sin(B / 2 / r);
	}
	
	
	public static void main (String [] args){
		Scanner scan = new Scanner(System.in);
		
		while (true){
			double length = scan.nextDouble();
			double tempChange = scan.nextDouble();
			double coef = scan.nextDouble();
			
			if (length < 0 && tempChange < 0 && coef < 0){
				break;
			}
			
			if (tempChange == 0 || coef == 0){
				System.out.println("0.000");
				continue;
			}
			
			double newLength = length * (1 + tempChange * coef);
			
			//System.out.println(length + " " + newLength);
			
			double r = equationSolver(length, newLength);
			//System.out.println(r);
			
			double angle = newLength / r;
			
			double result = r * (1-Math.cos(angle / 2));
		
			result = Math.round(result * 1000d) / 1000d;
			
			DecimalFormat formatter = new DecimalFormat("0.000");
			System.out.println(formatter.format(result));
		}

		
		scan.close();
	}
}