About how many common shares were there in total for all years?
{"2017": {"Total Cash Dividends Paid": 119.7, "Total Cash Dividends Paid Per Common Share": 0.64}, "2018": {"Total Cash Dividends Paid": 102.9, "Total Cash Dividends Paid Per Common Share": 0.64}, "2019": {"Total Cash Dividends Paid": 99.1, "Total Cash Dividends Paid Per Common Share": 0.64}, "Total": {"Total Cash Dividends Paid": 321.7, "Total Cash Dividends Paid Per Common Share": ""}}
total_cash_dividends = df["Total"]["Total Cash Dividends Paid"]
common_share_dividends = df["2017"]["Total Cash Dividends Paid Per Common Share"]
answer = total_cash_dividends / common_share_dividends