Sum of cosines

Geometry Level 5

$A=\cos\left(\frac{13\pi}{20}\right) +\cos\left(\frac{21\pi}{20}\right) +\cos\left(\frac{29\pi}{20}\right) +\cos\left(\frac{37\pi}{20}\right)$

Find the value of $\lfloor 1000A \rfloor$ .

Notation: $\lfloor \cdot \rfloor$ denotes the floor function.