The term "Ultimate Net Loss" shall mean the sum actually paid by the Reinsured in respect of any Loss Occurrence including expenses of litigation, if any, and all other loss expenses of the Reinsured,(excluding,however, office expenses and salaries of employees of the Reinsured) but whether collected or not, other than underlying Excess of Loss reinsurances, if any, shall be first deducted from such loss to arrive at the amount of liability, if any, attaching hereunder.