$\frac{3+\frac{1}{2}}{2+\frac{1}{3}}\times \frac{4-\frac{1}{3}}{3-\frac{1}{4}}\times \frac{5+\frac{1}{4}}{4+\frac{1}{5}}\times \frac{6-\frac{1}{5}}{5-\frac{1}{6}}\times \dots \times \frac{2019+\frac{1}{2018}}{2018+\frac{1}{2019}}\times \frac{2020-\frac{1}{2019}}{2019-\frac{1}{2020} }$

这题我做了半天都做不出来，求大神教一下