/* Problem4 */
#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std; 

double arctan(double x, int n);
 
int main(int argc, char *argv[])
{ int n; 
  double x, pi;
  do {
  cout<<"Dose to x kai to plhthos orwn n ths seiras: ";
  cin>>x>>n;
  }while ((-1>x || x>1) || n<=0);
  
  pi=16*arctan(1.0/5,n)-4*arctan(1.0/239,n);
  cout<<"H Gwnia se bathmous einai: "<<arctan(x,n)*180/pi<<endl;
  cout<<"H proseggistikh timh to pi einai: "<<pi<<endl;  
  
  system("Pause");
  return 0;
}

double arctan(double x, int n)
{double ser=0;
 for(int i=0; i<=n; i++)
    ser=ser+pow(-1.0,i)*pow(x,2*i+1)/(2*i+1);
 return ser;
 }