???Where can I find a doctor that allows euthanasia???

lets face it death cancer brain tumours are all traggic and painful way to die. I want to find a doctor that allows euthanasia for when I die it won't be so painful. Obvoiusly since I'm young I have alot of time to find one. I don't want to suicide that's not what this is about I just want to find a doctor that allows euthanasia so when I die I can die peacefully in my sleep. It's my life I'll do what I want with it and I know there are some countries that allow quick and easy deaths so I begin my search where can I find a doctor that will?? Don't hold out on me I'm going to do it when I'm old anyway and theres nothing you can say that'll change my mind ok?