system("aria2c https://s3.amazonaws.com/assets.datacamp.com/production/course_10628/slides/chapter1.pdf")
system("aria2c https://s3.amazonaws.com/assets.datacamp.com/production/course_10628/slides/chapter2.pdf")
system("aria2c https://s3.amazonaws.com/assets.datacamp.com/production/course_10628/slides/chapter3.pdf")
system("aria2c https://s3.amazonaws.com/assets.datacamp.com/production/course_10628/slides/chapter4.pdf")
todo 先阅读 slides 有一定的思路先