#include<iostream>
#include<math.h>
#define PI (3.141592657)
using namespace std;

typedef struct Point{
	double x,y;
}Point;

double LengthOfTwoPoints(Point x,Point y){
	double dx=x.x-y.x,dy=x.y-y.y;
	return sqrt(dx*dx+dy*dy);
}


double CaculateAngle(Point a,Point b,Point c){
	double la = LengthOfTwoPoints(b,c);
	double lb = LengthOfTwoPoints(a,c);
	double lc = LengthOfTwoPoints(a,b);
	return acos((lb*lb+lc*lc-la*la)/(2*lb*lc));
}

double LengthOfArc(double angle,double radius){
	return angle*radius;
}

double LengthOfRope(Point nails[],int N,double radius){
	double totalLength=0;
	int prePos=0,nextPos=0;
	if(N==1) return 2*PI*radius;
	for(int i=0;i<N;i++){
		prePos=i-1,nextPos=i+1;
		if(prePos<0) prePos=N-1;
		if(nextPos>=N) nextPos=0;
		totalLength+=LengthOfTwoPoints(nails[i],nails[nextPos])
			+LengthOfArc(PI-CaculateAngle(nails[i],nails[prePos],nails[nextPos]),radius);
	}
	return totalLength;
}

/*double LengthOfRope(Point nails[],int N,double radius){
	double totalLength=2*PI*radius;
	int nextPos=0;
	if(N==1)
		return totalLength;
	for(int i=0;i<N;i++){
		nextPos=i+1;
		if(nextPos>=N) nextPos=0;
		totalLength+=LengthOfTwoPoints(nails[i],nails[nextPos]);
	}
	return totalLength;
}*/

int main(){
	Point nails[100];
	int N=0;
	double radius=0;
	scanf("%d%lf",&N,&radius);
	for(int i=0;i<N;i++)
		scanf("%lf%lf",&nails[i].x,&nails[i].y);
	printf("%.2lf",LengthOfRope(nails,N,radius));
	return 0;
}