context: According to the annual passenger flow, which in 2012 amounted to 1,443,735,000 people (excluding passenger traffic on the light rail), the Hong Kong Metro ranks 4th in China and 10th in the world. The average passenger flow per day is about 3 944 631 people.
question: How many people use the metro in Hong Kong per day according to 2019?
answers.text: 3 944 631