import static java.lang.Math.*;
import static java.util.Arrays.*;
import java.util.*;

public class Main {
	Scanner sc = new Scanner(System.in);
	double INF = Double.POSITIVE_INFINITY;
	
	void run() {
		while (sc.hasNext()) {
			int W = sc.nextInt(), H = sc.nextInt(), N = sc.nextInt();
			if ((W|H|N) == 0) return;
			int[] xs = new int[N * 2 + 2], ys = new int[N * 2 + 2];
			for (int i = 0; i < N * 2; i++) {
				xs[i] = sc.nextInt();
				ys[i] = sc.nextInt();
			}
			xs[N * 2] = xs[N * 2 + 1] = W;
			ys[N * 2 + 1] = H;
			ArrayList<Double> list = new ArrayList<Double>();
			list.add(0.0);
			list.add((double)H);
			for (int i = 0; i < xs.length; i++) {
				for (int j = 0; j < i; j++) if (xs[i] != xs[j]) {
					double y = (double)(xs[i] * ys[j] - xs[j] * ys[i]) / (xs[i] - xs[j]);
					if (0 < y && y < H) list.add(y);
				}
			}
			Collections.sort(list);
			double res = 0;
			for (int i = 0; i < list.size() - 1; i++) {
				double sy = list.get(i), ty = list.get(i + 1);
				double y = (sy + ty) / 2;
				double[] ds = new double[N * 2];
				for (int j = 0; j < N * 2; j++) {
					if (xs[j] == 0) {
						if (ys[j] >= y) ds[j] = INF;
						else ds[j] = -INF;
					} else {
						ds[j] = (ys[j] - y) / xs[j];
					}
				}
				sort(ds);
				double s = min(H, max(0, y + ds[N - 1] * W));
				double t = min(H, max(0, y + ds[N] * W));
				res += (t - s) * (ty - sy) / (H * H);
			}
			System.out.printf("%.10f%n", res);
		}
	}
	
	public static void main(String[] args) {
		new Main().run();
	}
}