ural 1020 Rope

 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\n",ans);

39     return 0;

40 }

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