12.5.2 Olympic algebra

Problem: Calculate the sum: \[ \begin{array}{l} \left(\frac{1+2}{3}+\frac{4+5}{6}+\frac{7+8}{9}+\cdots+\frac{2017+2018}{2019}\right)+ \\ +\left(1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{673}\right) . \end{array} \]