Let the function $$f:[0, 1] \rightarrow R$$ be defined by $$f(x) = \frac{4^x}{4^x + 2}$$. Then the value of $$f\left(\frac{1}{40}\right)+f\left(\frac{2}{40}\right)+f\left(\frac{3}{40}\right)+.....+f\left(\frac{39}{40}\right) - f\left(\frac{1}{2}\right)$$ is__________.