What is the difference between capital stock value in class A and B shares?
{"Capital stock -- Parent Company": {"Number of shares": "Number of shares", "Capital stock (SEK million)": "Capital stock (SEK million)"}, "Capital stock -- Class A shares": {"Number of shares": 261755983, "Capital stock (SEK million)": 1309}, "Capital stock -- Class B shares": {"Number of shares": 3072395752, "Capital stock (SEK million)": 15363}, "Capital stock -- Total": {"Number of shares": 3334151735, "Capital stock (SEK million)": 16672}}
capital_stock_class_b = df["Capital stock -- Class B shares"]["Capital stock (SEK million)"]
capital_stock_class_a = df["Capital stock -- Class A shares"]["Capital stock (SEK million)"]
answer = capital_stock_class_b - capital_stock_class_a