حاصل عبارت $\frac{\frac{1}{2} - \frac{1}{3}}{\frac{1}{3} - \frac{1}{4}} \times \frac{\frac{1}{4} - \frac{1}{5}}{\frac{1}{5} - \frac{1}{6}} \times \frac{\frac{1}{6} - \frac{1}{7}}{\frac{1}{7} - \frac{1}{8}} \times \dots \times \frac{\frac{1}{48} - \frac{1}{49}}{\frac{1}{49} - \frac{1}{50}}$ کدام است؟