#include <iostream>

   using namespace std;

int main()
{
 	 // computation of pi:
		int N = 1000;
  	 	double pi_quart = 0.0;
 		double counter = -1.0;
      		for (int n=0;n<N;n++)
            	{
			counter = - 1.0 * counter;
    			double denominator = 2.0 * n + 1;
    			pi_quart += counter/denominator;
		}

  		double pi = 4.0 * pi_quart;
  		cout << "Computed value of pi after " << N << " terms " <<
		"is " << pi <<  endl; 
   return 0;
}