What is the total prepaid expenses made in 2018 and 2019?
{"December 31, -- ": {"2019": 2019, "2018": 2018}, "December 31, -- Prepaid expenses": {"2019": 1948, "2018": 1179}, "December 31, -- Securities litigation insurance receivable": {"2019": 16627, "2018": 306}, "December 31, -- Other current assets": {"2019": 1556, "2018": 2865}, "December 31, -- Prepaid expenses and other current assets": {"2019": 20131, "2018": 4350}}
total_2019 = df["December 31, -- Prepaid expenses"]["2019"]
total_2018 = df["December 31, -- Prepaid expenses"]["2018"]
answer = total_2019 + total_2018