Georg has $2n + 1$ cards with one number written on each card. On one card the integer $0$ is written, and among the rest of the cards, the integers $k = 1, ... , n$ appear, each twice. Georg wants to place the cards in a row in such a way that the $0$-card is in the middle, and for each $k = 1, ... , n$, the two cards with the number $k$ have the distance $k$ (meaning that there are exactly $k - 1$ cards between them). For which $1 \le n \le 10$ is this possible?