uva11186

 1 #include<set>
 2 #include<map>
 3 #include<queue>
 4 #include<stack>
 5 #include<cmath>
 6 #include<vector>
 7 #include<string>
 8 #include<cstdio>
 9 #include<cstring>
10 #include<iomanip>
11 #include<stdlib.h>
12 #include<iostream>
13 #include<algorithm>
14 using namespace std;
15 #define eps 1E-8
16 /*注意可能会有输出-0.000*/
17 #define Sgn(x) (x<-eps? -1 :x<eps? 0:1)//x为两个浮点数差的比较,注意返回整型
18 #define Cvs(x) (x > 0.0 ? x+eps : x-eps)//浮点数转化
19 #define zero(x) (((x)>0?(x):-(x))<eps)//判断是否等于0
20 #define mul(a,b) (a<<b)
21 #define dir(a,b) (a>>b)
22 typedef long long ll;
23 typedef unsigned long long ull;
24 const int Inf=1<<28;
25 const ll INF=1ll<<60;
26 const double Pi=acos(-1.0);
27 const int Mod=1e9+7;
28 const int Max=10010;
29 double g[Max];
30 int main()
31 {
32 int n,r;
33 while(~scanf("%d %d",&n,&r))
34 {
35     if(!n&&!r)
36         break;
37     for(int i=0;i<n;++i)
38     {
39         scanf("%lf",&g[i]);
40         g[i]=g[i]/180*Pi;
41     }
42     sort(g,g+n);
43     double ans=0;
44     for(int i=0;i<n;++i)
45     {
46         for(int j=i+1;j<n;++j)
47         {
48             ans+=(n+2*i-2*j)*1.0*sin(g[j]-g[i]);
49         }
50     }
51     ans=ans*r*r*0.5;
52     printf("%.0f\n",ans);
53 }
54 return 0;
55 }