#define MIN(x,y) (x < y ? x : y)
	#define MAX(x,y) (x > y ? x : y)

	double t,tol,x,y,s,m;

   tol = pow(0.5,27),
   s = 0,
   m = 1;
   x = MAX(a,b);
   y = MIN(a,b);
   while (x - y > tol * y) {
      t = (x + y) / 2;
      y = sqrt(x * y);
      x = t;
      m *= 2;
      s += m * (x - y) * (x - y);
   }
   len = M_PI * ((a + b) * (a + b) - s) / (x + y);