What is the increase/ (decrease) in number of common shares beneficially owned of Silicon Integrated Systems Corp. from April 14, 2018 to April 14, 2019?
{"": {"As of April 14, 2018": "Number of common shares beneficially owned", "As of April 14, 2019": "Number of common shares beneficially owned"}, "Name of Beneficial Owner -- Hsun Chieh Investment Co., Ltd. (1)": {"As of April 14, 2018": 3.5, "As of April 14, 2019": 3.64}, "Name of Beneficial Owner -- Silicon Integrated Systems Corp.": {"As of April 14, 2018": 2.5, "As of April 14, 2019": 2.35}, "Name of Beneficial Owner -- Directors and executive officers as a group": {"As of April 14, 2018": 6.32, "As of April 14, 2019": 6.67}}
common_shares_2019 = df["Name of Beneficial Owner -- Silicon Integrated Systems Corp."]["As of April 14, 2019"]
common_shares_2018 = df["Name of Beneficial Owner -- Silicon Integrated Systems Corp."]["As of April 14, 2018"]
answer = common_shares_2019 - common_shares_2018