A body moves on a frictionless plane starting from rest. If \( S_n \) is the distance moved between \( t = n - 1 \) and \( t = n \) and \( S_{n-1} \) is the distance moved between \( t = n - 2 \) and \( t = n - 1 \), then the ratio \( \frac{S_{n-1}}{S_n} \) is \( \left(1 - \frac{2}{x}\right) \) for \( n = 10 \). The value of \( x \) is _________.