Cash Flow from Operating Activities The decrease in operating cash flows for 2007 resulted from timing of cash flows associated with our Medicare Part D offerings, offset by Medicare enrollment growth and improved earnings.
During 2007, we paid $725.5 million to CMS under the risk corridor terms of our 2006 contracts with CMS.
Similarly, the provision for net amounts payable under the risk corridor terms of our 2007 contracts with CMS, which will be paid in 2008, was $102.6 million.
The increase in operating cash flows for 2006 compared to 2005 resulted from Medicare enrollment growth, improved earnings, and the timing of cash flows associated with our Medicare Part D offerings which were new beginning January 1, 2006.
Our 2006 Part D results related to both stand-alone PDP and MA-PD offerings reflected provisions for net amounts payable to CMS under the risk corridor terms of our contracts with CMS.
This risk corridor amount, which was paid in 2007 as discussed above, reflects favorable experience on allowable risk corridor costs during the second half of 2006 compared to the expectations set out in our original annual bid for 2006 contracts with CMS.
The favorable experience was associated with the Medicare Part D portion of our MA-PD offerings as well as our Standard and Enhanced stand-alone plans.
Comparisons of our operating cash flows also are impacted by other changes in our working capital.
The most significant drivers of changes in our working capital are typically the timing of receipts for premiums and ASO fees and payments of benefit expenses.
We illustrate these changes with the following summaries of receivables and benefits payable.
The detail of total net receivables was as follows at December 31, 2007, 2006 and 2005:
## Table 0 ##
Military services base receivables consist of estimated claims owed from the federal government for health care services provided to beneficiaries and underwriting fees.
The claim reimbursement component of military services base receivables is generally collected over a three to four month period.
The timing of claim reimbursements resulted in the decrease in base receivables from 2006 to 2007 as well as from 2005 to 2006.
The $28.0 million decrease in military services change order receivables from 2005 to 2006 resulted from the collection of receivables in 2006 related to an equitable adjustment to the contract price negotiated in late 2005 for services not originally specified in the contract.
Humana Inc.  NOTES TO CONSOLIDATED FINANCIAL STATEMENTS—(Continued) the Humana common stock fund.
However, a participant could reinvest any funds, including the Company match in the Humana common stock fund, in any other plan investment option at any time.
Beginning January 1, 2007, the Company’s cash match is invested pursuant to the participant’s contribution direction.
Stock-Based Compensation We have plans under which options to purchase our common stock and restricted stock awards have been granted to executive officers, directors, key employees and consultants.
The terms and vesting schedules for stock-based awards vary by type of grant.
Generally, the awards vest upon time-based conditions.
Upon exercise, stock-based compensation awards are settled with authorized but unissued company stock.
The compensation expense that has been charged against income for these plans was as follows for the years ended December 31, 2007, 2006, and 2005:
## Table 1 ##
Since 2006, a greater proportion of the awards granted to employees, excluding executive officers, were restricted stock awards as opposed to stock options when compared to grants made in prior years.
The tax benefit recognized in our consolidated financial statements is based on the amount of compensation expense recorded for book purposes.
The actual tax benefit realized in our tax return is based on the intrinsic value, or the excess of the market value over the exercise or purchase price, of stock options exercised and restricted stock awards vested during the period.
The actual tax benefit realized for the deductions taken on our tax returns from option exercises and restricted stock vesting totaled $48.0 million in 2007, $47.8 million in 2006, and $22.3 million in 2005.
There was no capitalized stock-based compensation expense.
Beginning April 2006, the stock plans provide that one restricted share is equivalent to 1.7 stock options.
At December 31, 2007, there were 15,774,996 shares reserved for stock award plans, including 9,994,245 shares of common stock available for future grants assuming all stock options or 5,878,968 shares available for future grants assuming all restricted shares.
Stock Options Stock options are granted with an exercise price equal to the average market value of the underlying common stock on the date of grant.
Our stock plans, as approved by the Board of Directors and stockholders, define average market value as the average of the highest and lowest stock prices reported by the New York Stock Exchange on a given date.
Exercise provisions vary, but most options vest in whole or in part 1 to 3 years after grant and expire 7 to 10 years after grant.
Upon grant, stock options are assigned a fair value based on the Black-Scholes valuation model.
Compensation expense is recognized on a straight-line basis over the total requisite service period, generally the total vesting period, for the entire award.
VA health care delivery system through our network of providers.
We are compensated by the VA for the cost of our providers’ services at a specified contractual amount per service plus an additional administrative fee for each transaction.
The contract, under which we began providing services on January 1, 2008, is comprised of one base period and four one-year option periods subject to renewals at the federal government’s option.
We are currently in the first option period, which expires on September 30, 2009.
For the year ended December 31, 2008, revenues under this VA contract were approximately $22.7 million, or less than 1% of our total premium and ASO fees.
For the year ended December 31, 2008, military services premium revenues were approximately $3.2 billion, or 11.3% of our total premiums and ASO fees, and military services ASO fees totaled $76.8 million, or 0.3% of our total premiums and ASO fees.
International and Green Ribbon Health Operations In August 2006, we established our subsidiary Humana Europe in the United Kingdom to provide commissioning support to Primary Care Trusts, or PCTs, in England.
Under the contracts we are awarded, we work in partnership with local PCTs, health care providers, and patients to strengthen health-service delivery and to implement strategies at a local level to help the National Health Service enhance patient experience, improve clinical outcomes, and reduce costs.
For the year ended December 31, 2008, revenues under these contracts were approximately $7.7 million, or less than 1% of our total premium and ASO fees.
We participated in a Medicare Health Support pilot program through Green Ribbon Health, or GRH, a jointventure company with Pfizer Health Solutions Inc.  GRH was designed to support CMS assigned Medicare beneficiaries living with diabetes and/or congestive heart failure in Central Florida.
GRH used disease management initiatives, including evidence-based clinical guidelines, personal self-directed change strategies, and personal nurses to help participants navigate the health system.
Revenues under the contract with CMS over the period which began November 1, 2005 and ended August 15, 2008 are subject to refund unless savings, satisfaction, and clinical improvement targets are met.
Under the terms of the contract, after a claims run-out period, CMS is required to deliver a performance report during the third quarter of 2009.
To date, all revenues have been deferred until reliable estimates are determinable, and revenues are not expected to be material when recognized.
Our Products Marketed to Commercial Segment Employers and Members Smart Plans and Other Consumer Products Over the last several years, we have developed and offered various commercial products designed to provide options and choices to employers that are annually facing substantial premium increases driven by double-digit medical cost inflation.
These Smart plans, discussed more fully below, and other consumer offerings, which can be offered on either a fully-insured or ASO basis, provided coverage to approximately 670,000 members at December 31, 2008, representing approximately 18.5% of our total commercial medical membership as detailed below.
## Table 2 ##
These products are often offered to employer groups as “bundles”, where the subscribers are offered various HMO and PPO options, with various employer contribution strategies as determined by the employer.

<table><tr><td></td><td></td><td></td><td></td><td colspan="2">Change</td></tr><tr><td></td><td>2007</td><td>2006</td><td>2005</td><td>2007</td><td>2006</td></tr><tr><td></td><td colspan="5">(in thousands)</td></tr><tr><td>Military services:</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Base receivable</td><td>$404,570</td><td>$452,509</td><td>$509,444</td><td>$-47,939</td><td>$-56,935</td></tr><tr><td>Change orders</td><td>5,168</td><td>4,247</td><td>32,285</td><td>921</td><td>-28,038</td></tr><tr><td>Military services subtotal</td><td>409,738</td><td>456,756</td><td>541,729</td><td>-47,018</td><td>-84,973</td></tr><tr><td>Medicare</td><td>137,345</td><td>143,875</td><td>66,536</td><td>-6,530</td><td>77,339</td></tr><tr><td>Commercial and other</td><td>126,718</td><td>125,899</td><td>162,944</td><td>819</td><td>-37,045</td></tr><tr><td>Allowance for doubtful accounts</td><td>-68,260</td><td>-45,589</td><td>-32,557</td><td>-22,671</td><td>-13,032</td></tr><tr><td>Total net receivables</td><td>$605,541</td><td>$680,941</td><td>$738,652</td><td>-75,400</td><td>-57,711</td></tr><tr><td>Reconciliation to cash flow statement:</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Provision for doubtful accounts</td><td></td><td></td><td></td><td>28,922</td><td>20,901</td></tr><tr><td>Receivables from acquisition</td><td></td><td></td><td></td><td>-14,267</td><td>-843</td></tr><tr><td>Change in receivables per cash flow statement resulting in cash from operations</td><td></td><td></td><td></td><td>$-60,745</td><td>$-37,653</td></tr></table>
<table><tr><td></td><td>2007</td><td>2006</td><td>2005</td></tr><tr><td></td><td colspan="3">(in thousands)</td></tr><tr><td>Stock-based compensation expense by type:</td><td></td><td></td><td></td></tr><tr><td>Stock options</td><td>$15,408</td><td>$18,025</td><td>$24,304</td></tr><tr><td>Restricted stock awards</td><td>26,724</td><td>14,533</td><td>5,849</td></tr><tr><td>Total stock-based compensation expense</td><td>42,132</td><td>32,558</td><td>30,153</td></tr><tr><td>Tax benefit recognized</td><td>-15,732</td><td>-12,028</td><td>-11,337</td></tr><tr><td>Stock-based compensation expense, net of tax</td><td>$26,400</td><td>$20,530</td><td>$18,816</td></tr></table>
<table><tr><td></td><td>Smart Plans and Other Consumer Membership</td><td>Other Commercial Membership</td><td>Commercial Medical Membership</td></tr><tr><td>Fully-insured</td><td>392,500</td><td>1,586,300</td><td>1,978,800</td></tr><tr><td>ASO</td><td>277,500</td><td>1,364,500</td><td>1,642,000</td></tr><tr><td>Total Commercial medical</td><td>670,000</td><td>2,950,800</td><td>3,620,800</td></tr></table>

Question: Between 2007 and 2006,how many years does Total net receivables decrease?