"Yes, that's definitely meant to be parsed as a four and ten. Which means only three flights of stairs." She lets the key go and then is in the stairwell, holding onto the railing and keeping the door open with her foot. The period during which the other girl might see her walking over there and opening the door is astoundingly brief. Kanaya realizes too late that she's dipped into her insane fastness attribute again, and flashes her companion an uneasy apologetic grin. This is the most annoying thing about being around other people: They have to pace themselves. It takes forever. It's the only thing for which she has to wait anymore. Though of course it pales in comparison to waiting for death.