容易发现是圆心的凸包再加上一个圆的周长。

#include<bits/stdc++.h>
using namespace std;
const int N=1e4+5;
const int dx[4]={1,-1,-1,1};
const int dy[4]={1,1,-1,-1};
const double Pi=acos(-1);
struct point{
	double x,y;
}p[4*N],sta[4*N];
double cross(point a,point b,point c){
	return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
}
double dis(point a,point b){
	return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int len,top=0;
bool cmp(point n1,point n2){
	if(n1.x!=n2.x)return n1.x<n2.x;
	return n1.y<n2.y;
}
double Andrew(){
	sort(p+1,p+len+1,cmp);
	for(int i=1;i<=len;i++){
		while(top>1&&cross(sta[top-1],sta[top],p[i])<=0)top--;
		sta[++top]=p[i];
	}
	int t=top;
	for(int i=len-1;i>=1;i--){
		while(top>t&&cross(sta[top-1],sta[top],p[i])<=0)top--;
		sta[++top]=p[i];
	}
	double res=0;
	for(int i=2;i<=top;i++){
		res=res+dis(sta[i-1],sta[i]);
	}
	return res;
}
double getx(double x,double y,double rad){
	return x*cos(rad)-y*sin(rad);
}
double gety(double x,double y,double rad){
	return x*sin(rad)+y*cos(rad);
}
int main(){
	int n;scanf("%d",&n);
	double a,b,r;scanf("%lf%lf%lf",&a,&b,&r);
	a=a/2-r,b=b/2-r;
	for(int i=1;i<=n;i++){
		double x,y,rad;
		scanf("%lf%lf%lf",&x,&y,&rad);
		for(int j=0;j<4;j++){
			double tx=getx(b*dx[j],a*dy[j],rad);
			double ty=gety(b*dx[j],a*dy[j],rad);
			p[++len]={x+tx,y+ty};
		}
	}
	printf("%.2lf",Andrew()+2*Pi*r);
	return 0;
}