code: public function run($input) {
  		list($part_number, $part_step) = $input;
  		$x=0.0;
  		$sum=0.0;
  		for ($i = $part_number; $i < $this->num_steps; $i += $part_step) {
  			$x = ($i + 0.5) * $this->step;
  			$sum += 4.0 / (1.0 + $x * $x);
  		}
  		return $sum;
  	}
docs: run the work
  
  @param \Serializable $input the data, that the worker should process
  @return \Serializable Returns the result
  @throws \Exception in case of a processing Error an Exception will be thrown