What is the increase/ (decrease) in Q1 days from 2018 to 2020?
{"": {"Q1": "Days", "Q2": "Days", "Q3": "Days", "Q4": "Days"}, "2018": {"Q1": 90, "Q2": 91, "Q3": 91, "Q4": 93}, "2019": {"Q1": 89, "Q2": 91, "Q3": 91, "Q4": 94}, "2020": {"Q1": 88, "Q2": 91, "Q3": 91, "Q4": 96}}
q1_2020 = df["2020"]["Q1"]
q1_2018 = df["2018"]["Q1"]
answer = q1_2020 - q1_2018