[Int] fibs := [1,1];

Int length([Int] xs) {
	if (xs.nil) {
		return 0;
	} else {
		return 1 + length(xs.tl);
	}
}

Int get([Int] xs, Int i) {
	if (i == 0) {
		return xs.hd;
	} else {
		return get(xs.tl, i-1);
	}
}

[Int] append([Int] xs, [Int] ys) {
	if (xs.nil) {
		return ys;
	} else {
		return xs.hd : append(xs.tl, ys);
	}
}

Bool gt(Int x, Int y) {
	if (x == 0) {
		return False;
	} else if (y == 0) {
		return True;
	} else {
		return gt(x-1, y-1);
	}
}

Int fib(Int n) {
	if (gt(length(fibs), n - 1)) {
		return get(fibs, n - 1);
	} else {
		Int fn := fib(n-1) + fib(n-2);
		fibs := append(fibs, [fn]);
		return fn;
	}
}

Int main() {
	return fib(92); // Largest to fit in a 64-bit integer
}