1 #include <cstdio> 2 #include <cstring> 3 #include <cmath> 4 #include <algorithm> 5 #define maxn 2000 6 using namespace std; 7 const double pi=acos(-1.0); 8 9 double sqr(double x) 10 { 11 return x*x; 12 } 13 struct node 14 { 15 double x,y; 16 }p[maxn]; 17 18 double dis(node a,node b) 19 { 20 return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y)); 21 } 22 int main() 23 { 24 int n; 25 double r; 26 scanf("%d%lf",&n,&r); 27 for(int i=0; i<n; i++) 28 { 29 scanf("%lf%lf",&p[i].x,&p[i].y); 30 } 31 p[n]=p[0]; 32 double ans=0; 33 for(int i=1; i<=n; i++) 34 { 35 ans+=dis(p[i],p[i-1]); 36 } 37 ans+=pi*r*2; 38 printf("%.2lf ",ans); 39 return 0; 40 }