Q54

Consider a function $f:(0,1) \rightarrow\{0,1\}$ defined as follows. For a real number $r \in(0,1), f(r)=1$ if the second digit after the decimal point in $r$ is one of the four digits $2,3,6$ and $7$. Otherwise, $f(r)$ is equal to $0$. The number of points in $(0,1)$ at which $f$ is discontinuous is $\_\_\_\_\_\_$. (answer in integer)