$\frac{1}{\sqrt{25}-\sqrt{24}}-\frac{1}{\sqrt{24}-\sqrt{23}}+\frac{1}{\sqrt{23}-\sqrt{22}}-\frac{1}{\sqrt{22}-\sqrt{21}}+\frac{1}{\sqrt{21}-\sqrt{20}}$ का सरलीकृत मान क्या है -