30 lines
471 B
C++
30 lines
471 B
C++
#include<cstdio>
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#include<cmath>
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#include<algorithm>
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using namespace std;
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const double Pi=acos(-1);
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int n,r;
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double res,g[505];
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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while(scanf("%d%d",&n,&r)==2&&n)
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{
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for(int i=0;i<n;i++)
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{
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scanf("%lf",&g[i]);
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g[i]=g[i]/180*Pi;
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}
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sort(g,g+n);
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res=0;
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for(int i=0;i<n;i++)
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for(int j=i+1;j<n;j++)
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res+=(n+2*i-2*j)*sin(g[j]-g[i]);
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res=res*r*r/2;
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printf("%.0lf\n",res);
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}
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return 0;
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}
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