From x to y

Let $x$ and $y$ be integers such that $1<x\leq y$ , and the function $f$ be defined as

$f(x,y)=\displaystyle\prod_{k=x}^y \left(1-\frac{1}{k}\right)$

If $S=\displaystyle\sum_{k=2}^{2014} {f(k, 2014)}$ , then the exact value of $S$ can be expressed as a mixed number $a\frac{b}{c}$ , where $a$ is a positive integer and $b$ and $c$ are positive coprime integers. What is the value of $a-10b-10c$ ?