UVA 10432 (Polygon Inside A Circle)

/***
	Md. Nazmul Hasan
	Shahjalal University of Science & Technology,Sylhet.
	hasan08sust@gmail.com
	***/
	#include<iostream>
	#include<cstdio>
	#include<stack>
	#include<queue>
	#include<map>
	#include<vector>
	#include<algorithm>
	#include<cstring>
	#include<sstream>
	#include<cmath>
	#include <iomanip>
	using namespace std ;
	typedef long long ll ;
	typedef int in ;
	typedef unsigned long long ull ;
	const double pi = 2*acos(0) ;
	#define maxi 40000
	#define pf printf
	#define sc scanf
	#define pb push_back
	#define MEM(x,y) (memset((x),(y),sizeof(x)))
	#define MIN(x,y) ((x) < (y) ? (x) : (y))
	#define MAX(x,y) ((x) > (y) ? (x) : (y))
	#define load(array,size) for(int i=0 ; i<size ; i++) cin>>array[i] ;
	#define new_line pf("\n")
	#define clear_data(array) memset(array,0,sizeof(array))
	#define highest_int 2147483647
	int main()
	{
	double r,n,d,angle,area;
	while(sc("%lf %lf",&r,&n)==2){
	d =(n*r*r)/2.0;
	//cout<<d<<endl;
	angle = (2/n)*pi;
	//cout<<angle<<endl;
	area = d * sin(angle);
	pf("%.3lf\n",area);
	}
	return 0;
	}