Biogen Inc. /zigman2/quotes/201531540/composite BIIB +2.19% did a good job buying low, as the biotechnology company's stock rally on Tuesday has boosted the value of the shares repurchased over the past six months by about $708.6 million. The company said it bought back 3.1 million shares for a total value of approximately $718 million, which implies an average price paid of $231.61 per share. With the stock soaring 27% to $283.45, after the company said it would pursue regulatory approval of its treatment for Alzheimer's disease and following a big earnings beat, it would now take $878.7 million to buy back 3.1 million shares, or about $161.7 million more than Biogen paid. During the second quarter, the company had bought 10.4 million shares for about $2.4 billion, implying an average price paid of $230.77 per share. At current prices, it would cost $2.95 billion to buyback 10.4 million shares. The stock had plunged in March after the company said it would discontinue Phase 3 trials of its Alzheimer's drug. The stock has still lost 5.6% year to date, while the Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA -0.07% has gained 15.2%.