What is the percentage change in  Share buybacks from during the year 2018 to during the year 2019?
{"As per January 1: -- Issued shares": {"2018": 62297394, "2019": 56297394}, "As per January 1: -- Treasury shares": {"2018": 6157241, "2019": 6978496}, "As per January 1: -- Outstanding shares": {"2018": 56140153, "2019": 49318898}, "Changes during the year: -- Cancellation of treasury shares": {"2018": 6000000, "2019": 5000000}, "Changes during the year: -- Share buybacks": {"2018": 7242734, "2019": 950902}, "Changes during the year: -- Treasury shares used for share based performance programs": {"2018": 421479, "2019": 498224}, "As per December 31: -- Issued shares": {"2018": 56297394, "2019": 51297394}, "As per December 31: -- Treasury shares": {"2018": 6978496, "2019": 2431174}, "As per December 31: -- Outstanding shares": {"2018": 49318898, "2019": 48866220}}
share_buybacks_2019 = df["Changes during the year: -- Share buybacks"]["2019"]
share_buybacks_2018 = df["Changes during the year: -- Share buybacks"]["2018"]
answer = (share_buybacks_2019 - share_buybacks_2018) / share_buybacks_2018 * 100.0