What was the change in the Net operating loss carryforwards from 2018 to 2019?
{"Deferred tax assets: -- Net operating loss carryforwards": {"2019": 35120, "2018": 24159}, "Deferred tax assets: -- Share-based compensation": {"2019": 5687, "2018": 2760}, "Deferred tax assets: -- Deferred revenue": {"2019": 1761, "2018": 2237}, "Deferred tax assets: -- Fixed assets  ": {"2019": 4187, "2018": 3593}, "Deferred tax assets: -- Lease liability  ": {"2019": 11748, "2018": 17024}, "Deferred tax assets: -- Accrued compensation  ": {"2019": 1211, "2018": 742}, "Deferred tax assets: -- Accrued costs  ": {"2019": 401, "2018": 1362}, "Deferred tax assets: -- Deferred rent  ": {"2019": 320, "2018": 473}, "Deferred tax assets: -- Income tax credits  ": {"2019": 1833, "2018": 1151}, "Deferred tax assets: -- Other  ": {"2019": 1247, "2018": 109}, "Deferred tax assets: -- Gross deferred tax assets  ": {"2019": 63515, "2018": 53610}, "Deferred tax liabilities:         -- Prepaid expenses  ": {"2019": -219, "2018": -315}, "Deferred tax liabilities:         -- Fixed assets  ": {"2019": -13855, "2018": -19280}, "Deferred tax liabilities:         -- Unremitted earnings  ": {"2019": -320, "2018": -115}, "Deferred tax liabilities:         -- Intangible assets  ": {"2019": -4818, "2018": "\u2014"}, "Deferred tax liabilities:         -- Capitalized commissions  ": {"2019": -7606, "2018": "\u2014"}, "Deferred tax liabilities:         -- Other  ": {"2019": -387, "2018": "\u2014"}, "Deferred tax liabilities:         -- Gross deferred tax liabilities  ": {"2019": -27205, "2018": -19710}, "Deferred tax liabilities:         -- Valuation allowance  ": {"2019": -38318, "2018": -34008}, "Deferred tax liabilities:         -- Deferred tax (liabilities) assets, net ": {"2019": -2008, "2018": -108}}
net_operating_loss_2019 = df["Deferred tax assets: -- Net operating loss carryforwards"]["2019"]
net_operating_loss_2018 = df["Deferred tax assets: -- Net operating loss carryforwards"]["2018"]
answer = net_operating_loss_2019 - net_operating_loss_2018