What was the increase / (decrease) in trade accounts receivable less than 60 days past due?
{"(In thousands of Canadian dollars)": {"2019": "$", "2018": "$"}, "Less than 60 days past due": {"2019": 18645, "2018": 32857}, "60 to 90 days past due": {"2019": 899, "2018": 3022}, "More than 90 days past due": {"2019": 3074, "2018": 4923}, "": {"2019": 22618, "2018": 40802}}
trade_accounts_receivable_2019 = df["Less than 60 days past due"]["2019"]
trade_accounts_receivable_2018 = df["Less than 60 days past due"]["2018"]
answer = trade_accounts_receivable_2019 - trade_accounts_receivable_2018