"There are about 700 milligrams of cyanide per kilogram of apple seeds. If the average apple seed has a mass of 0.7 grams, then this means there 0.49 mg of cyanogenic compounds per pip."
2mg per kg is a lethal dose.
i'd do 5 seeds per kg to be safe. for example, if every apple had 5 seeds (i would count beforehand) then that's 50 apple cores for 50kg or 80 apples for 80kg.
these also must be chewed/crushed so that it's more easily absorbed which makes it even less palatable.
if you are 66 lbs or 30kg, then this would be a viable option in theory. in practice you would also want to take an antiemetic before to ensure you won't vomit it all up. you also might want a sedative like a benzo because cyanide can be very uncomfortable and painful. a benzo would also reduce the risk of seizing.
there are plenty of other options besides this, but it is definitely possible to ctb by apple seeds.