Tính giá trị biểu thức:
$A=\left ( 1-\frac{1}{6} \right )\left ( 1-\frac{1}{10} \right )\left ( 1-\frac{1}{15} \right )\left ( 1-\frac{1}{21} \right )\left ( 1-\frac{1}{28} \right )\left ( 1-\frac{1}{36} \right )\left ( 1-\frac{1}{45} \right )\left ( 1-\frac{1}{55} \right )...\left ( 1-\frac{1}{2025078} \right )$