import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.function.Function;

public class O1753 {

	public static void main(String[] args) throws IOException {
		BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
		String[] s = r.readLine().split(" ");
		int h = Integer.parseInt(s[0]), H = Integer.parseInt(s[1]), L = Integer.parseInt(s[2]);
		if(h >= H / 2) {
			System.out.println(0);
			return;
		}
		Function<Double, Double> func = (a) -> { // H * Cos(a) / 2 - h * Ctg(a)
			double cos = Math.cos(a);
			return H * cos / 2 - h * cos / Math.sin(a);
		};
		Function<Double, Double> derivative = (a) -> { //h * Csc^2(a) - H * Sin(a)/2
			double sin = Math.sin(a);
			return h / (sin * sin) - H * sin / 2;
		};
		final double EPS = 1e-7;
		double start = Math.asin(h / H);
		double end = Math.PI / 2;
		while(end > start) {
			double x = (start + end) / 2;
			double val = derivative.apply(x);
			if(val > EPS) {
				start = x;
			} else if(val < -EPS) {
				end = x;
			} else {
				end = x;
				break;
			}
		}
		System.out.println(func.apply(end));
	}

}