What is the increase / (decrease) in the network advertising from 2018 to 2019?
{"Network advertising": {"2019": 22.7, "2018": 28.2}, "Broadcast station": {"2019": 11.9, "2018": 10.8}, "Network distribution": {"2019": 4.9, "2018": 4.8}, "Other": {"2019": 2.3, "2018": 1.6}, "Total revenue from contracts with customers": {"2019": 41.8, "2018": 45.4}, "Other revenue": {"2019": "-", "2018": "-"}, "Total Broadcasting segment revenue": {"2019": 41.8, "2018": 45.4}}
network_advertising_2019 = df["Network advertising"]["2019"]
network_advertising_2018 = df["Network advertising"]["2018"]
answer = network_advertising_2019 - network_advertising_2018