#include "stdio.h"
#include "math.h"
int main()
{
	int i;
	double a,b,r,x,y,nx,ny,len;
	scanf("%d %lf",&i,&r);
	if(i>0)
	scanf("%lf %lf",&a,&b);
	x=a;
	y=b;
	len=0.0;
	while(i>1){
		scanf("%lf %lf",&nx,&ny);
		x-=nx;
		y-=ny;
		len=sqrt(x*x+y*y);
		x=nx;
		y=ny;
		i--;
	}
	if(i>0)
	len+=2*3.1415926535897932384626*r;
	printf("%.2f\n",len);
	return 0;
}