A group of students play the following game: they are counting one by one from $00$ to $99$ taking turns, but instead of every number they only say one of its digits. (The numbers in order are $00$, $01$, $02$, $...$., meaning that one-digit numbers are regarded as two-digit numbers with a first digit $0$.) One way of starting the counting could be for example $0$, $1$, $2$, $0$, $4$, $0$, $6$, $7$, $8$, $9,$ $1$, $1$, $2$, $1$, $1$, $5$, $6$, $1$, $8$, $1$, $0$, $2$ etc. When they reach $99$, the counting restarts from $00$. At some point Csongor enters the room and after listening to the counting for a while, he discovers that he is able to tell what number the counting is at. How many digits has Csongor heard at least?