#include <iostream>
#include <cstdio>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <utility>
#include <numeric>
#include <algorithm>
#include <functional>
#include <cctype>
#include <complex>
#include <string>
#include <sstream>
#include <fstream>
#include <cassert>
using namespace std;

//common
typedef int  i32;
typedef long long i64,ll;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii;
typedef long long ll; typedef vector<long long> vl; typedef pair<long long,long long> pll; typedef vector<pair<long long,long long> > vpll;
typedef vector<string> vs; typedef long double ld;

#define BR "\n"
#define ALL(c) (c).begin(),(c).end()
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))

//config
//#undef NDEBUG
//#define INF 1<<30
//#define EPS 1e-8
//const ll MOD =100000007;

//debug
#ifdef NDEBUG
#define DUMP(x)
#define DUMPLN(x)
#define DEBUG(x)
#define DEBUGLN(x)
#define LINE()
#define LINELN()
#define CHECK(exp,act)
#define STOP(e)
#else
#define DUMP(x)  cerr << #x << " = " << (x)
#define DUMPLN(x)  DUMP(x) <<endl
#define DEBUG(x) DUMP(x) << LINE() << " " << __FILE__
#define DEBUGLN(x) DEBUG(x)<<endl
#define LINE()    cerr<< " (L" << __LINE__ << ")"
#define LINELN()    LINE()<<endl
#define CHECK(exp,act)  if(exp!=act){DUMPLN(exp);DEBUGLN(act);}
#define STOP(e)  CHECK(e,true);if(!(e)) exit(1);
#endif

template<class T> inline string toString(const vector<T>& x) {
	stringstream ss;
	REP(i,x.size()){
		if(i!=0)ss<<" ";
		ss<< x[i];
	}
	return ss.str();
}

template<class T> inline string toString(const vector<vector<T> >& map) {
	stringstream ss;
	REP(i,map.size()){
		if(i!=0)ss<<BR;
		ss<< toString(map[i]);
	}
	return ss.str();
}
template<class K,class V>  string toString(map<K,V>& x) {
	string res;stringstream ss;
	for(auto& p:x)ss<< p.first<<":" << p.second<<" ";
	return ss.str();
}

string BITtoString(int bit){
    stringstream ss;
    while(bit!=0){ss<<(bit%2);bit/=2;}
    string res=ss.str();reverse(ALL(res));
    return res;
}

template<typename T,typename V> inline T mod(T v,V MOD){
	return (v%MOD+MOD)%MOD;
}

namespace Ps{
	const double EPS=1e-10;
	const double INF=1e12;
	typedef complex<double> P;
#define X real()
#define Y imag()

	double cross(const P& a,const P& b){
		return imag(conj(a)*b);
	}
}
using namespace Ps;
namespace std{
	bool operator < (const P& a,const P& b){
		return a.X !=b.X?a.X<b.X:a.Y<b.Y;
	}

	bool operator == (const P& a,const P& b){
		return hypot(a.X-b.X,a.Y-b.Y)<EPS;
	}
}


namespace Ls{
	using namespace Ps;
	struct L: public vector<P>{
		L(const P& a,const P &b){
			push_back(a);push_back(b);
		}
	};

	P crosspoint(const L&l,const L&m){
		double A=cross(l[1]-l[0],m[1]-m[0]);
		double B=cross(l[1]-l[0],l[1]-m[0]);
		if(abs(A)<EPS && abs(B)<EPS)return m[0];
		if(abs(A)<EPS) throw exception();
		return m[0]+B/A*(m[1]-m[0]);
	}
}
using namespace Ls;
class Main{
public:

	void run(){
		// ifstream cin("in");
		// ofstream cout("out");
		while(true){
			int W,H,N;cin >> W >> H >> N;if(W==0 && H==0 && N==0)break;
			vector<P> ps(2*N);
			REP(i,2*N){
				double x,y;cin >> x >> y;
				ps[i]=P(x,y);
			}

			vector<P> lps;
			lps.push_back(P(0,0));lps.push_back(P(0,H));
			REP(i,2*N){
				REP(j,2*N)if(i<j){
					try{
						lps.push_back(crosspoint(L(ps[i],ps[j]),L(P(0,0),P(0,H))));						
					}catch(exception){}
				}
				try{
					lps.push_back(crosspoint(L(ps[i],P(W,0)),L(P(0,0),P(0,H))));				
				}catch(exception){}				
				try{
					lps.push_back(crosspoint(L(ps[i],P(W,H)),L(P(0,0),P(0,H))));
				}catch(exception){}	
			}
			sort(ALL(lps));
			lps.erase(unique(ALL(lps)),lps.end());
			{
				vector<P> tmp;
				REP(i,lps.size())if(0-EPS<=lps[i].Y && lps[i].Y<= H+EPS){
					tmp.push_back(lps[i]);
				}
				lps=tmp;
			}
			// y

			double res=0;
			REP(i,lps.size()-1){
				P ld=lps[i],lu=lps[i+1];
				P lm=(ld+lu)*0.5;
				vector<pair<double,int>> rps;
				REP(j,ps.size()){
					rps.push_back(make_pair(arg(ps[j]-lm),j));
				}
				sort(ALL(rps));
				P rd,ru;
                try{
                	rd=crosspoint(L(lm,ps[rps[N-1].second]),L(P(W,0),P(W,H)));
                }catch(exception){
                	rd=P(W,0);
                }
                try{
                	ru=crosspoint(L(lm,ps[rps[N].second]),L(P(W,0),P(W,H)));
                }catch(exception){
                	ru=P(W,H);
                }
               	res+=abs((lu.Y-ld.Y)*(max(0.0,min(1.0*H,ru.Y))-max(0.0,min(1.0*H,rd.Y))));
   		    }
   		    cout << fixed << setprecision(18);
			cout << res/H/H << endl;
		}
	}
};

 int main(){
ios::sync_with_stdio(false);
 	Main().run();
 	return 0;
 }

Measured memory_bytes: 2236