Get a Parameter Value in Oak

so if I set up a router like this

router.get("/:id", (ctx) => {/*handle router context*/})

router.get("/:id", (ctx) => {/*handle router context*/})

router.get("/:id", (ctx) => {/*handle router context*/})

router.get("/:id", (ctx) => {/*handle router context*/})

then how do I get the value of the id parameter? I have tried ctx.id and it did not accept it