Exhibit A:

Mr. Epstein also directly owns a director stock option to purchase 17,900 shares
of Class A common stock with (i) an exercise price of $121.43 per share and (ii)
an expiration date of April 30, 2024. Of the 17,900 shares subject to this
option, 5,400 shares vested on April 30, 2016, 6,250 shares vested on April 30,
2017, and 6,250 shares are scheduled to vest on April 30, 2018.

Mr. Epstein also directly owns a director stock option to purchase 5,000 shares
of Class A common stock with (i) an exercise price of $175.98 per share and (ii)
an expiration date of May 31, 2025.  Of the 5,000 shares subject to this option,
1,250 shares vested on May 31, 2016, 1,250 shares vested on May 31, 2017, 1,250
shares are scheduled to vest on May 31, 2018, and 1,250 shares are scheduled to
vest on May 31, 2019.

Mr. Epstein also directly owns a director stock option to purchase 5,000 shares
of Class A common stock with (i) an exercise price of $186.54 per share and (ii)
an expiration date of May 31, 2026.  Of the 5,000 shares subject to this option,
1,250 shares vested on May 31, 2017, 1,250 shares are scheduled to vest on May
31, 2018, 1,250 shares are scheduled to vest on May 31, 2019, and 1,250 shares
are scheduled to vest on May 31, 2020.