#include <stdio.h>

#define NSTEPS 20000000000

int main()
{
  double pi, sum, step, x;
  long int i;

  sum = 0;

  step = 1.0 / (double)NSTEPS;

  for (i=1; i<=NSTEPS; i++)
    {
      x = step * ((double)i-0.5);
      sum += 4.0/(1.0+x*x);
    }
  pi = sum * step;

  printf("Pi is %4.12f\n", pi);

  return 0;
}