What is the increase/ (decrease) in Weighted average number of common shares from 2018 to 2019?
{"": {"2019": "$", "2018": "$", "2017": "$"}, "Net loss attributable to shareholders of Teekay Corporation for basic loss per share": {"2019": -310577, "2018": -79237, "2017": -163276}, "Reduction in net earnings due to dilutive impact of stock-based compensation in Teekay LNG, Altera and Teekay Tankers and stock purchase warrants in Altera": {"2019": "\u2014", "2018": "\u2014", "2017": -90}, "Net loss attributable to shareholders of Teekay Corporation for diluted loss per share": {"2019": -310577, "2018": -79237, "2017": -163366}, "Weighted average number of common shares": {"2019": 100719224, "2018": 99670176, "2017": 86335473}, "Dilutive effect of stock-based compensation": {"2019": "\u2014", "2018": "\u2014", "2017": "\u2014"}, "Common stock and common stock equivalents": {"2019": 100719224, "2018": 99670176, "2017": 86335473}, "Loss per common share - basic and diluted": {"2019": -3.08, "2018": -0.79, "2017": -1.89}}
weighted_average_2019 = df["Weighted average number of common shares"]["2019"]
weighted_average_2018 = df["Weighted average number of common shares"]["2018"]
answer = weighted_average_2019 - weighted_average_2018