#include<stdio.h>
#include<math.h>
#define P 3.1415927
int main(){
    float x,y,xo,yo,a,b,c;
    double l;
    int n,i,r;
    scanf("%d%d",&n,&r);
    scanf("%f%f",&x,&y);
    a=x;
    b=y;
    l=0;
    for(i=1;i<n;i++){
        scanf("%f%f",&xo,&yo);
        x-=xo;
        y-=yo;
        l+=sqrt(x*x+y*y);
        x=xo;
        y=yo;
    }
    x-=a;
    y-=b;
    l+=sqrt(x*x+y*y);
	c=360*n-(n-2)*180-n*180;
    l+=(2*P*r*c)/360;
    printf("%.2f\n",l);
    return 0;
}

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