/* calculation of pi: approximating a circle by polygons */
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
   double sum = 0.;
   double numerator = 1./sqrt(3.);
	cout << "     n \t\t pi(calc) \t\t diff" << endl;

   for(int n=0;n<=30;n++)
    {   sum += numerator/(2.*(double)n+1.);
        numerator *= -1./3.;
		cout <<   setw(10) << n << "\t" << setprecision(18) << sum*6. << "\t" << fabs(M_PI-sum*6.) << endl;
    }
}