The first problem is designed to be accessible with some insight required to obtain full marks.

The first subtask can be hard-coded. That is, the following table can be calculated by hand and a solution can mimic looking up the correct output in the table.

$N$	$1$	$2$	$3$	$4$	$5$	$6$	$7$	$8$	$9$	$10$
Output	$0$	$0$	$0$	$1$	$1$	$0$	$0$	$1$	$1$	$1$

For the second and third subtasks, we can notice that we need $N=4a+5b$ for non-negative integers $a$ and $b$ where $a\le \frac{n}{4}$ and $b\le \frac{n}{5}$. This means we can try all possible values for $a$ and $b$ using two nested loops.

For a full solution, we can loop through only all possible values of $a$ to determine if there is a corresponding value of $b$. For each of these values $i$, this is equivalent to checking if $N-4i$ is divisible by $5$. Alternatively, we take a similar approach but loop through only all possible values of $b$.

There is also a clever extremely quick solution that involves extending the table listed above for the first subtask to $N=20$ and considering the quotient and remainder when $N$ is divided by $20$.