> #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;
> }