If all the room numbers are meant to have 4 digits, and the four digits are achieved by formatting numbers less than 1000 with custom format "0000", then you can use

=LEFT(TEXT(A1,"0000"),2)

If all the room numbers are meant to have 4 digits, and the four digits are achieved by formatting numbers less than 1000 with custom format "0000", then you can use

=LEFT(TEXT(A1,"0000"),2)

Edit: FWIW, this approach also works if the value is text.