#include <math.h>

int main(argc,argv)
int argc;
char *argv[];
{
  int done = 0, n, i;
  double PI25DT = 3.141592653589793238462643;
  double pi, h, sum, x;
  
  while (!done)
    {
      printf("Enter the number of intervals: (0 quits)\n");
      scanf("%d",&n);
      if (n == 0) break;
      
      h   = 1.0 / (double) n;
      sum = 0.0;
      for (i = 1; i <= n; i++) {
	x = h * ((double)i - 0.5);
	sum += 4.0 / (1.0 + x*x);
      }
      pi = h * sum;
      
      printf("pi is approximately %.16f, Error is %.16f\n",
	     pi, fabs(pi - PI25DT));
    }

  return 0;
}