How much do the top 3 contractual obligation terms add up to in 2020?
{"Long-term debt: (a) -- Principal payments": {"2020": 5518, "2021-2022": 11744, "2023-2024": 8000, "Thereafter": 47519, "Total": 72781}, "Long-term debt: (a) -- Interest payments": {"2020": 2299, "2021-2022": 4309, "2023-2024": 3818, "Thereafter": 29383, "Total": 39809}, "Long-term debt: (a) -- Construction commitments (b)": {"2020": 3443, "2021-2022": 515, "2023-2024": 0, "Thereafter": 0, "Total": 3958}, "Long-term debt: (a) -- Operating leases, including imputed interest (c)": {"2020": 1790, "2021-2022": 3144, "2023-2024": 2413, "Thereafter": 3645, "Total": 10992}, "Long-term debt: (a) -- Finance leases, including imputed interest (c)": {"2020": 797, "2021-2022": 2008, "2023-2024": 2165, "Thereafter": 9872, "Total": 14842}, "Long-term debt: (a) -- Transition tax (d)": {"2020": 1180, "2021-2022": 2900, "2023-2024": 4168, "Thereafter": 8155, "Total": 16403}, "Long-term debt: (a) -- Purchase commitments (e)": {"2020": 17478, "2021-2022": 1185, "2023-2024": 159, "Thereafter": 339, "Total": 19161}, "Long-term debt: (a) -- Other long-term liabilities (f)": {"2020": 0, "2021-2022": 72, "2023-2024": 29, "Thereafter": 324, "Total": 425}, "Long-term debt: (a) -- Total": {"2020": 32505, "2021-2022": 25877, "2023-2024": 20752, "Thereafter": 99237, "Total": 178371}}
top_3_terms = [
    "Long-term debt: (a) -- Principal payments",
    "Long-term debt: (a) -- Purchase commitments (e)",
    "Long-term debt: (a) -- Construction commitments (b)"
]
total = 0
for term in top_3_terms:
    total += df[term]["2020"]
answer = total