What was the change in the expense for share-based payment for  Stefan Ries  in 2019 from 2018?
{"Christian Klein (Co-CEO from 10/10/2019)": {"2019": 1925.0, "2018": 442.2}, "Jennifer Morgan (Co-CEO from 10/10/2019)": {"2019": 2894.0, "2018": 796.1}, "Robert Enslin (until 4/5/2019)": {"2019": 3480.0, "2018": 727.0}, "Adaire Fox-Martin": {"2019": 2667.0, "2018": 796.1}, "Michael Kleinemeier": {"2019": 3253.0, "2018": 914.2}, "Bernd Leukert (until 3/31/2019)": {"2019": 8606.0, "2018": 775.2}, "Bill McDermott (CEO until 10/10/2019, Executive Board member until 11/15/2019)": {"2019": 14689.0, "2018": 2155.8}, "Luka Mucic": {"2019": 3391.0, "2018": 675.8}, "Jrgen Mller (from 1/1/2019)": {"2019": 768.0, "2018": "-"}, "Stefan Ries": {"2019": 2646.0, "2018": 772.0}, "Thomas Saueressig (from 11/1/2019)": {"2019": 128.0, "2018": "-"}, "Total": {"2019": 44446.5, "2018": 8054.4}}
stefan_ries_2019 = df["Stefan Ries"]["2019"]
stefan_ries_2018 = df["Stefan Ries"]["2018"]
answer = stefan_ries_2019 - stefan_ries_2018