ural 1020 Rope

 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <algorithm>
 #define maxn 2000
 using namespace std;
 const double pi=acos(-1.0);

 double sqr(double x)
 {
     return x*x;
 }
 struct node
 {
     double x,y;
 }p[maxn];

 double dis(node a,node b)
 {
     return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y));
 }
 int main()
 {
     int n;
     double r;
     scanf("%d%lf",&n,&r);
     for(int i=; i<n; i++)
     {
         scanf("%lf%lf",&p[i].x,&p[i].y);
     }
     p[n]=p[];
     double ans=;
     for(int i=; i<=n; i++)
     {
         ans+=dis(p[i],p[i-]);
     }
     ans+=pi*r*;
     printf("%.2lf\n",ans);
     return ;
 }