#include<bits/stdc++.h>

#define int long long
#define x first
#define y second
#define endl '\n'

using namespace std;

const int N=1e6+10,INF=1e14,mod=998244353,M=2e5+10;
const double eps = 1e-8;
typedef pair<double,double> PII;
typedef pair<PII,int> PIII;

int gcd(int a,int b){
	return b?gcd(b,a%b):a;
}

int qmi(int a,int k){
	int res=1;
	while(k){
		if(k&1) res=res*a%mod;
		a=a*a%mod;
		k>>=1;
	}
	return res;
}

PII a[N];

PII operator-(PII t1,PII t2){
	PII c={t1.x-t2.x,t1.y-t2.y};
	return c;
}
PII operator+(PII t1,PII t2){
	PII c={t1.x+t2.x,t1.y+t2.y};
	return c;
}

int sign(double x){
	if (fabs(x) < eps) return 0;
	if (x < 0) return -1;
	return 1;
}

double cross(PII t1,PII t2){return t1.x*t2.y-t1.y*t2.x;}

double dot(PII a,PII b){
	return a.x * b.x + a.y * b.y;
}

double get_length(PII a){
	return sqrt(dot(a, a));
}

double distance_to_line(PII p, PII a, PII b){
	PII v1 = b - a, v2 = p - a;
	return fabs(cross(v1, v2) / get_length(v1));
}

double dts(PII p, PII a, PII b){
	if (a == b) return get_length(p - a);
	PII v1 = b - a, v2 = p - a, v3 = p - b;
	if (sign(dot(v1, v2)) < 0) return get_length(v2);
	if (sign(dot(v1, v3)) > 0) return get_length(v3);
	return distance_to_line(p, a, b);
}

bool check(double p1,double p2){
	if(sign(p1-p2)>=0) return true;//那就是可以
	return false;
}

bool check1(PII x1,PII x2,PII x3,PII nei){
	if(cross(x2-x1,nei-x1)<=0)return false;
	if(cross(x3-x2,nei-x2)<=0) return false;
	if(cross(x1-x3,nei-x3)<=0) return false;
	return true;
}

void slove(){
	int n;cin>>n;
	int cx,cy,rr;cin>>cx>>cy>>rr;
	PII dian={cx,cy};
	double cr=rr;
	for(int i=1;i<=n;i++){
		int c1,c2;cin>>c1>>c2;
		a[i]={c1,c2};
	}
	
	int l=1,r=1;
	double area=0;
	double ans=0;
	for(int i=1;i<=n;i++){
		if(l+2<=r){
			int p=r%n;if(!p) p=n;
			area-=fabs(cross(a[i]-a[i-1],a[p]-a[i-1]));
		}
		l=i,r=max(r,l+1);
		int p1=(r+1)%n;if(!p1) p1=n;
		int p2=(r)%n;if(!p2) p2=n;
		while(check(dts(dian,a[l],a[p1]),cr)&&!check1(a[l],a[p2],a[p1],dian)){
			area+=fabs(cross(a[p1]-a[l],a[p2]-a[l]));
			r++;
			p1=(r+1)%n;if(!p1) p1=n;
			p2=(r)%n;if(!p2) p2=n;
		} 
		ans=max(ans,area);
	}
	ans+=eps;
	int q=ans*1;
	cout<<q<<endl;
}
signed main(){
	ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
	int T=1;
//	cin>>T;
	while(T--) slove();
}