#includeusing namespace std; const double PI=acos(-1.0); int main() { int r,k; while(scanf("%d%d",&r,&k)!=EOF) printf("%.3fn",0.5*r*r*sin(2*PI/k)*k); return 0; }
#includeusing namespace std; const double PI=acos(-1.0); int main() { int r,k; while(scanf("%d%d",&r,&k)!=EOF) printf("%.3fn",0.5*r*r*sin(2*PI/k)*k); return 0; }
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