AMERICAN TOWER CORPORATION AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS As of December 31, 2010, total unrecognized compensation expense related to unvested restricted stock units granted under the 2007 Plan was $57.5 million and is expected to be recognized over a weighted average period of approximately two years.
Employee Stock Purchase Plan —The Company maintains an employee stock purchase plan (“ESPP”) for all eligible employees.
Under the ESPP, shares of the Company’s Common Stock may be purchased during bi-annual offering periods at 85% of the lower of the fair market value on the first or the last day of each offering period.
Employees may purchase shares having a value not exceeding 15% of their gross compensation during an offering period and may not purchase more than $25,000 worth of stock in a calendar year (based on market values at the beginning of each offering period).
The offering periods run from June 1 through November 30 and from December 1 through May 31 of each year.
During the 2010, 2009 and 2008 offering periods employees purchased 75,354, 77,509 and 55,764 shares, respectively, at weighted average prices per share of $34.16, $23.91 and $30.08, respectively.
The fair value of the ESPP offerings is estimated on the offering period commencement date using a Black-Scholes pricing model with the expense recognized over the expected life, which is the six month offering period over which employees accumulate payroll deductions to purchase the Company’s Common Stock.
The weighted average fair value for the ESPP shares purchased during 2010, 2009 and 2008 was $9.43, $6.65 and $7.89, respectively.
At December 31, 2010, 8.7 million shares remain reserved for future issuance under the plan.
Key assumptions used to apply this pricing model for the years ended December 31, are as follows:
## Table 0 ##
13.
STOCKHOLDERS’ EQUITY Warrants—In August 2005, the Company completed its merger with SpectraSite, Inc.  and assumed outstanding warrants to purchase shares of SpectraSite, Inc.  common stock.
As of the merger completion date, each warrant was exercisable for two shares of SpectraSite, Inc.  common stock at an exercise price of $32 per warrant.
Upon completion of the merger, each warrant to purchase shares of SpectraSite, Inc.  common stock automatically converted into a warrant to purchase shares of the Company’s Common Stock, such that upon exercise of each warrant, the holder has a right to receive 3.575 shares of the Company’s Common Stock in lieu of each share of SpectraSite, Inc.  common stock that would have been receivable under each assumed warrant prior to the merger.
Upon completion of the Company’s merger with SpectraSite, Inc. , these warrants were exercisable for approximately 6.8 million shares of Common Stock.
Of these warrants, warrants to purchase approximately none and 1.7 million shares of Common Stock remained outstanding as of December 31, 2010 and 2009, respectively.
These warrants expired on February 10, 2010.
Stock Repurchase Program—During the year ended December 31, 2010, the Company repurchased an aggregate of approximately 9.3 million shares of its Common Stock for an aggregate of $420.8 million, including commissions and fees, of which $418.6 million was paid in cash prior to December 31, 2010 and $2.2 million was included in accounts payable and accrued expenses in the accompanying consolidated balance sheet as of December 31, 2010, pursuant to its publicly announced stock repurchase program, as described below.
Simon Property Group, Inc.  Simon Property Group, L. P.  Notes to Consolidated Financial Statements (Dollars in thousands, except share, per share, unit and per unit amounts and where indicated as in millions or billions) 102 Management Fees and Other Revenues Management fees and other revenues are generally received from our unconsolidated joint venture properties as well as third parties.
Management fee revenue is earned based on a contractual percentage of joint venture property revenue.
Development fee revenue is earned on a contractual percentage of hard costs to develop a property.
Leasing fee revenue is earned on a contractual per square foot charge based on the square footage of current year leasing activity.
We recognize revenue for these services provided when earned based on the underlying activity.
Revenues from insurance premiums charged to unconsolidated properties are recognized on a pro-rata basis over the terms of the policies.
Insurance losses on these policies and our self-insurance for our consolidated properties are reflected in property operating expenses in the accompanying consolidated statements of operations and comprehensive income and include estimates for losses incurred but not reported as well as losses pending settlement.
Estimates for losses are based on evaluations by third-party actuaries and management’s estimates.
Total insurance reserves for our insurance subsidiaries and other self-insurance programs as of December 31, 2016 and 2015 approximated $83.5 million and $88.1 million, respectively, and are included in other liabilities in the consolidated balance sheets.
Information related to the securities included in the investment portfolio of our captive insurance subsidiaries is included within the “Marketable and Non-Marketable Securities” section above.
Allowance for Credit Losses We record a provision for credit losses based on our judgment of a tenant’s creditworthiness, ability to pay and probability of collection.
In addition, we also consider the retail sector in which the tenant operates and our historical collection experience in cases of bankruptcy, if applicable.
Accounts are written off when they are deemed to be no longer collectible.
Presented below is the activity in the allowance for credit losses during the following years:
## Table 1 ##
Income Taxes Simon and certain subsidiaries of the Operating Partnership have elected to be taxed as REITs under Sections 856 through 860 of the Internal Revenue Code and applicable Treasury regulations relating to REIT qualification.
In order to maintain this REIT status, the regulations require the entity to distribute at least 90% of REIT taxable income to its owners and meet certain other asset and income tests as well as other requirements.
We intend to continue to adhere to these requirements and maintain Simon’s REIT status and that of the REIT subsidiaries.
As REITs, these entities will generally not be liable for U. S.  federal corporate income taxes as long as they distribute in excess of 100% of their REIT taxable income.
Thus, we made no provision for U. S.  federal income taxes for these entities in the accompanying consolidated financial statements.
If Simon or any of the REIT subsidiaries fail to qualify as a REIT, Simon or that entity will be subject to tax at regular corporate rates for the years in which it failed to qualify.
If Simon or any of the REIT subsidiaries loses its REIT status it could not elect to be taxed as a REIT for four taxable years following the year during which qualification was lost unless the failure to qualify was due to reasonable cause and certain other conditions were satisfied.
We have also elected taxable REIT subsidiary, or TRS, status for some of our subsidiaries.
This enables us to provide services that would otherwise be considered impermissible for REITs and participate in activities that do not qualify as “rents from real property”.
For these entities, deferred tax assets and liabilities are established for temporary differences between the
Part II Item 5.
Market for the Registrant’s Common Equity, Related Stockholder Matters, and Issuer Purchases of Equity Securities Simon Market Information Simon’s common stock trades on the New York Stock Exchange under the symbol “SPG”.
The quarterly price range for the shares and the dividends declared per share for each quarter in the last two fiscal years are shown below:
## Table 2 ##
There is no established public trading market for Simon’s Class B common stock.
Dividends on the Class B common stock are identical to the common stock.
Holders The number of holders of record of common stock outstanding was 1,208 as of February 14, 2017.
The Class B common stock is subject to two voting trusts as to which Herbert Simon and David Simon are the trustees.
Shares of Class B common stock convert automatically into an equal number of shares of common stock upon the occurrence of certain events and can be converted into shares of common stock at the option of the holders.
Dividends We must pay a minimum amount of dividends to maintain Simon’s status as a REIT.
Simon’s future dividends and future distributions of the Operating Partnership will be determined by Simon’s Board of Directors, in its sole discretion, based on actual and projected financial condition, liquidity and results of operations, cash available for dividends and limited partner distributions, cash reserves as deemed necessary for capital and operating expenditures, financing covenants, if any, and the amount required to maintain Simon’s status as a REIT.
Common stock cash dividends during 2016 aggregated $6.50 per share.
Common stock cash dividends during 2015 aggregated $6.05 per share.
In January 2017, Simon’s Board of Directors declared a quarterly cash dividend of $1.75 per share of common stock payable on February 28, 2017 to stockholders of record on February 14, 2017.
We offer a dividend reinvestment plan that allows Simon’s stockholders to acquire additional shares by automatically reinvesting cash dividends.
Shares are acquired pursuant to the plan at a price equal to the prevailing market price of such shares, without payment of any brokerage commission or service charge.

Tables referenced above, in order (Table 0 first):
<table><tr><td></td><td>2010</td><td>2009</td><td>2008</td></tr><tr><td>Range of risk-free interest rate</td><td>0.22% - 0.23%</td><td>0.29% - 0.44%</td><td>1.99% - 3.28%</td></tr><tr><td>Weighted average risk-free interest rate</td><td>0.22%</td><td>0.38%</td><td>2.58%</td></tr><tr><td>Expected life of shares</td><td>6 months</td><td>6 months</td><td>6 months</td></tr><tr><td>Range of expected volatility of underlying stock price</td><td>35.26% - 35.27%</td><td>35.31% - 36.63%</td><td>27.85% - 28.51%</td></tr><tr><td>Weighted average expected volatility of underlying stock price</td><td>35.26%</td><td>35.83%</td><td>28.51%</td></tr><tr><td>Expected annual dividends</td><td>N/A</td><td>N/A</td><td>N/A</td></tr></table>
<table><tr><td></td><td colspan="3">For the Year Ended December 31,</td></tr><tr><td></td><td>2016</td><td>2015</td><td>2014</td></tr><tr><td>Balance, beginning of period</td><td>$30,094</td><td>$33,282</td><td>$32,681</td></tr><tr><td>Provision for credit losses</td><td>7,319</td><td>6,635</td><td>12,001</td></tr><tr><td>Accounts written off, net of recoveries</td><td>-14,915</td><td>-9,823</td><td>-11,400</td></tr><tr><td>Balance, end of period</td><td>$22,498</td><td>$30,094</td><td>$33,282</td></tr></table>
<table><tr><td></td><td>High</td><td>Low</td><td>Close</td><td>Declared Dividends</td></tr><tr><td>2015</td><td></td><td></td><td></td><td></td></tr><tr><td>1stQuarter</td><td>$206.31</td><td>$178.84</td><td>$195.64</td><td>$1.40</td></tr><tr><td>2ndQuarter</td><td>202.28</td><td>170.99</td><td>173.02</td><td>1.50</td></tr><tr><td>3rdQuarter</td><td>200.23</td><td>171.87</td><td>183.72</td><td>1.55</td></tr><tr><td>4thQuarter</td><td>208.14</td><td>180.55</td><td>194.44</td><td>1.60</td></tr><tr><td>2016</td><td></td><td></td><td></td><td></td></tr><tr><td>1stQuarter</td><td>$208.12</td><td>$176.11</td><td>$207.69</td><td>$1.60</td></tr><tr><td>2ndQuarter</td><td>217.17</td><td>190.82</td><td>216.90</td><td>1.60</td></tr><tr><td>3rdQuarter</td><td>229.10</td><td>206.02</td><td>207.01</td><td>1.65</td></tr><tr><td>4thQuarter</td><td>206.29</td><td>173.11</td><td>177.67</td><td>1.65</td></tr></table>

Question: What is the sum of 1stQuarter , 2ndQuarter and 3rdQuarter in 2015 for Low?
Answer: 521.7
Reasoning program: add(178.84,170.99), add(#0,171.87)