Steps for a token on a square to hit the trapdoor

Four corners of a square are labeled $1, 2, 3, 4$ in order, with edges $1\!-\!2$, $2\!-\!3$, $3\!-\!4$, $4\!-\!1$. A token steps to one of the two neighboring corners with equal probability each move. Corner $4$ is a trapdoor: the token stops when it lands there. It starts at corner $1$, which is adjacent to the trapdoor.

On average, how many steps until the token falls through corner $4$?