#include <iostream>
#include <math.h>
#include <iomanip>
 
using namespace std;
int n;
long long int k;
long double t1,t2,t3,b1,b2;
int main()
{
    cin >>n>>k;
    if (n==3)
    {
        long   double x1,x2,x3,y1,y2,y3;
        cin >> x1 >> y1;
        cin >> x2 >> y2;
        cin >> x3 >> y3;
        t1=sqrt(pow(x1-x2,2)+pow(y1-y2,2));
        t2=sqrt(pow(x3-x2,2)+pow(y3-y2,2));
        t3=sqrt(pow(x1-x3,2)+pow(y1-y3,2));
        long  double p,P;
        p=0.5*(t1+t2+t3);
        p=sqrt(p*(p-t1)*(p-t2)*(p-t3));
        P=p+k*(t1+t2+t3)+0.5*M_PI*pow(k,2);
        cout << fixed << setprecision(6)<<P<<endl;
    }
    else if (n==4)
    {
        long double p1,p2,p3,r1,r2,r3,p4,r4;
        cin >> p1 >> r1;
        cin >> p2 >> r2;
        cin >> p3 >> r3;
        cin >> p4 >> r4;
        b1=sqrt(pow(p1-p2,2)+pow(r1-r2,2));
        b2=sqrt(pow(p3-p2,2)+pow(r3-r2,2));
        long double P;
        P=b1*b2+k*(2*b1+2*b2)+M_PI*pow(k,2);
        cout << fixed << setprecision(6)<<P<<endl;
 
    }
    return 0;
}

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4 1
0 0
0 1
1 1
1 0