If you want to do medicine enough, apply for 4 med school places, and if you are one of the 60% of applicants who don't get in, take a gap year and apply again like everyone else. Only if you fail to get AAA will your 5th choice matter. And even then would you want a course that could lead to graduate medicine, or another path? But your PS will be 100% medicine so I'm really not sure what a maths dept will make of that! Do you even want to do a maths degree?