What is the total Trade receivables past due, net of allowance for doubtful accounts for 2019?
{"Trade receivables not past due": {"2019": 2082, "2018": 2091}, "Trade receivables past due, net of allowance for doubtful accounts -- Under 60 days": {"2019": 541, "2018": 508}, "Trade receivables past due, net of allowance for doubtful accounts -- 60 to 120 days": {"2019": 232, "2018": 304}, "Trade receivables past due, net of allowance for doubtful accounts -- Over 120 days": {"2019": 64, "2018": 72}, "Trade receivables past due, net of allowance for doubtful accounts -- Trade receivables, net of allowance for doubtful accounts": {"2019": 2919, "2018": 2975}}
total_under_60 = df["Trade receivables past due, net of allowance for doubtful accounts -- Under 60 days"]["2019"]
total_60_to_120 = df["Trade receivables past due, net of allowance for doubtful accounts -- 60 to 120 days"]["2019"]
total_over_120 = df["Trade receivables past due, net of allowance for doubtful accounts -- Over 120 days"]["2019"]
answer = total_under_60 + total_60_to_120 + total_over_120