(2) In 2013, our principal U. K subsidiary agreed with the trustees of one of the U. K.  plans to contribute an average of $11 million per year to that pension plan for the next three years.
The trustees of the plan have certain rights to request that our U. K.  subsidiary advance an amount equal to an actuarially determined winding-up deficit.
As of December 31, 2015, the estimated winding-up deficit was ￡240 million ($360 million at December 31, 2015 exchange rates).
The trustees of the plan have accepted in practice the agreed-upon schedule of contributions detailed above and have not requested the winding-up deficit be paid.
(3) Purchase obligations are defined as agreements to purchase goods and services that are enforceable and legally binding on us, and that specifies all significant terms, including what is to be purchased, at what price and the approximate timing of the transaction.
Most of our purchase obligations are related to purchases of information technology services or other service contracts.
(4) Excludes $12 million of unfunded commitments related to an investment in a limited partnership due to our inability to reasonably estimate the period(s) when the limited partnership will request funding.
(5) Excludes $218 million of liabilities for uncertain tax positions due to our inability to reasonably estimate the period(s) when potential cash settlements will be made.
Financial Condition At December 31, 2015, our net assets were $6.2 billion, representing total assets minus total liabilities, a decrease from $6.6 billion at December 31, 2014.
The decrease was due primarily to share repurchases of $1.6 billion, dividends of $323 million, and an increase in Accumulated other comprehensive loss of $289 million related primarily to an increase in the postretirement benefit obligation, partially offset by Net income of $1.4 billion for the year ended December 31, 2015.
Working capital increased by $77 million from $809 million at December 31, 2014 to $886 million at December 31, 2015.
Accumulated other comprehensive loss increased $289 million at December 31, 2015 as compared to December 31, 2014, which was primarily driven by the following: ?
negative net foreign currency translation adjustments of $436 million, which are attributable to the strengthening of the U. S.  dollar against certain foreign currencies, ?
a decrease of $155 million in net post-retirement benefit obligations, and ?
net financial instrument losses of $8 million.
REVIEW BY SEGMENT General We serve clients through the following segments: ?
Risk Solutions acts as an advisor and insurance and reinsurance broker, helping clients manage their risks, via consultation, as well as negotiation and placement of insurance risk with insurance carriers through our global distribution network.  ?
HR Solutions partners with organizations to solve their most complex benefits, talent and related financial challenges, and improve business performance by designing, implementing, communicating and administering a wide range of human capital, retirement, investment management, health care, compensation and talent management strategies.
Risk Solutions
## Table 0 ##
The demand for property and casualty insurance generally rises as the overall level of economic activity increases and generally falls as such activity decreases, affecting both the commissions and fees generated by our brokerage business.
The economic activity that impacts property and casualty insurance is described as exposure units, and is most closely correlated
Principal Financial Group, Inc.  Notes to Consolidated Financial Statements — (continued) 14.
Stockholders’ Equity — (continued) Reconciliation of Outstanding Shares
## Table 1 ##
On May 11, 2009, we issued 58.2 million shares of common stock at a price of $19.75 per share.
Net proceeds from the issuance were $1,109.1 million.
The proceeds from this offering will be used for general corporate purposes.
During November 2007, our Board of Directors authorized a share repurchase program of up to $500.0 million of our outstanding common stock.
On November 30, 2007, we entered into an accelerated common stock repurchase agreement with a third party investment bank for an aggregate purchase price of $250.0 million.
On this date, we paid $250.0 million and received the initial delivery of 2.9 million common shares, while retaining the right to receive additional common shares over the program’s execution period.
The accelerated common stock repurchase agreement was completed in January 2008, at which time we received 0.9 million additional common shares under this agreement.
In the fourth quarter of 2008, we suspended purchases of the remaining $250.0 million available under the November 2007 authorization.
Our Board of Directors has authorized various repurchase programs under which we are allowed to purchase shares of our outstanding common stock.
Shares repurchased under these programs are accounted for as treasury stock, carried at cost and reflected as a reduction to stockholders’ equity.
Accumulated Other Comprehensive Income (Loss) Comprehensive income includes all changes in stockholders’ equity during a period except those resulting from investments by stockholders and distributions to stockholders.
The components of accumulated other comprehensive income (loss) were as follows:
## Table 2 ##
Fair Value Measurement Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (an exit price).
The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels for disclosure purposes.
The fair value hierarchy gives the highest priority (Level 1) to quoted prices in active markets for identical assets or liabilities and gives the lowest priority (Level 3) to unobservable inputs.
An asset or liability’s classification within the fair value hierarchy is based on the lowest level of significant input to its valuation.
See Item 8.
‘‘Financial Statements and Supplementary Data, Notes to Consolidated Financial Statements, Note 15, Fair Value of Financial Instruments’’ for further details.
As of December 31, 2009, 37% of our net assets (liabilities) were Level 1, 58% were Level 2 and 5% were Level 3.
Excluding separate account assets as of December 31, 2009, 3% of our net assets (liabilities) were Level 1, 95% were Level 2 and 2% were Level 3.
As of December 31, 2008, 32% of our net assets (liabilities) were Level 1, 61% were Level 2 and 7% were Level 3.
Excluding separate account assets as of December 31, 2008, 2% of our net assets (liabilities) were Level 1, 95% were Level 2 and 3% were Level 3.
Changes in Level 3 fair value measurements The net change for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the year ended December 31, 2009, was as follows:
## Table 3 ##
The decrease in the fair value of Level 3 instruments for the year ended December 31, 2009, is primarily attributed to separate account assets.
The decrease in separate account assets is primarily a result of unrealized losses on real estate.
Unrealized losses on separate accounts do not impact net income in the consolidated statements of operations, as the change in value of separate account assets is offset by a change in value of separate account liabilities.
The net change for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the year ended December 31, 2008, was as follows:

Tables referenced above, in order (Table 0 first):
<table><tr><td>Years ended December 31(millions, except percentage data)</td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td>Revenue</td><td>$7,426</td><td>$7,834</td><td>$7,789</td></tr><tr><td>Operating income</td><td>1,506</td><td>1,648</td><td>1,540</td></tr><tr><td>Operating margin</td><td>20.3%</td><td>21.0%</td><td>19.8%</td></tr></table>
<table><tr><td> </td><td> Series A preferred stock</td><td> Series B preferred stock</td><td>Common stock</td></tr><tr><td> </td><td colspan="3">(in millions)</td></tr><tr><td>Outstanding shares at January 1, 2007</td><td>3.0</td><td>10.0</td><td>268.4</td></tr><tr><td>Shares issued</td><td>—</td><td>—</td><td>2.2</td></tr><tr><td>Treasury stock acquired</td><td>—</td><td>—</td><td>-11.5</td></tr><tr><td>Outstanding shares at December 31, 2007</td><td>3.0</td><td>10.0</td><td>259.1</td></tr><tr><td>Shares issued</td><td>—</td><td>—</td><td>1.2</td></tr><tr><td>Treasury stock acquired</td><td>—</td><td>—</td><td>-1.0</td></tr><tr><td>Outstanding shares at December 31, 2008</td><td>3.0</td><td>10.0</td><td>259.3</td></tr><tr><td>Shares issued</td><td>—</td><td>—</td><td>60.0</td></tr><tr><td>Treasury stock acquired</td><td>—</td><td>—</td><td>-0.3</td></tr><tr><td>Outstanding shares at December 31, 2009</td><td> 3.0</td><td> 10.0</td><td>319.0</td></tr></table>
<table><tr><td> </td><td>Net unrealized gains on available-for-sale securities</td><td>Net unrealized gains on derivative instruments</td><td>Foreign currency translation adjustment</td><td>Unrecognized postretirement benefit obligations</td><td>Accumulated other comprehensive income</td></tr><tr><td> </td><td colspan="5">(in millions)</td></tr><tr><td> Balances at January 1, 2007</td><td>$830.7</td><td>$28.3</td><td>$-26.6</td><td>$14.5</td><td>$846.9</td></tr><tr><td>Net change in unrealized gains on fixed maturities, available-for-sale</td><td>-991.4</td><td>—</td><td>—</td><td>—</td><td>-991.4</td></tr><tr><td>Net change in unrealized gains on equity securities, available-for-sale</td><td>-12.8</td><td>—</td><td>—</td><td>—</td><td>-12.8</td></tr><tr><td>Net change in unrealized gains on equity method subsidiaries and minority interest adjustments</td><td>68.4</td><td>—</td><td>—</td><td>—</td><td>68.4</td></tr><tr><td>Adjustments for assumed changes in amortization pattern</td><td>130.3</td><td>—</td><td>—</td><td>—</td><td>130.3</td></tr><tr><td>Net change in unrealized gains on derivative instruments</td><td>—</td><td>-25.7</td><td>—</td><td>—</td><td>-25.7</td></tr><tr><td>Change in net foreign currency translation adjustment</td><td>—</td><td>—</td><td>68.1</td><td>—</td><td>68.1</td></tr><tr><td>Change in unrecognized postretirement benefit obligations</td><td>—</td><td>—</td><td>—</td><td>81.1</td><td>81.1</td></tr><tr><td>Net change in provision for deferred income tax benefit (expense)</td><td>277.7</td><td>11.6</td><td>-5.6</td><td>-28.4</td><td>255.3</td></tr><tr><td> Balances at December 31, 2007</td><td>$302.9</td><td>$14.2</td><td>$35.9</td><td>$67.2</td><td>$420.2</td></tr></table>
<table><tr><td> </td><td>Balance as of December 31, 2009</td><td>Balance as of December 31, 2008</td><td>Net change</td></tr><tr><td> </td><td colspan="3">(in millions)</td></tr><tr><td> Assets</td><td></td><td></td><td></td></tr><tr><td>Total fixed maturities, available-for-sale</td><td>$1,172.6</td><td>$1,173.0</td><td>$-0.4</td></tr><tr><td>Fixed maturities, trading</td><td>63.5</td><td>60.7</td><td>2.8</td></tr><tr><td>Equity securities, available-for-sale</td><td>71.7</td><td>56.2</td><td>15.5</td></tr><tr><td>Derivative assets</td><td>54.4</td><td>100.7</td><td>-46.3</td></tr><tr><td>Separate account assets</td><td>4,120.7</td><td>6,042.3</td><td>-1,921.6</td></tr><tr><td> Liabilities</td><td></td><td></td><td></td></tr><tr><td>Investment-type insurance contracts</td><td>-23.6</td><td>-60.2</td><td>36.6</td></tr><tr><td>Derivative liabilities</td><td>-93.7</td><td>-266.9</td><td>173.2</td></tr><tr><td>Other liabilities</td><td>-89.1</td><td>-103.8</td><td>14.7</td></tr><tr><td> Net total</td><td>$5,276.5</td><td>$7,002.0</td><td>$-1,725.5</td></tr></table>

Question: Among 2007,2008 and 2009, which year is the Outstanding shares on December 31 for Common stock the most?
Answer: 2009