CF995B.Suit and Tie

Allen is hosting a formal dinner party. $2n$ people come to the event in $n$ pairs (couples). After a night of fun, Allen wants to line everyone up for a final picture. The $2n$ people line up, but Allen doesn't like the ordering. Allen prefers if each pair occupies adjacent positions in the line, as this makes the picture more aesthetic.

Help Allen find the minimum number of swaps of adjacent positions he must perform to make it so that each couple occupies adjacent positions in the line.

艾伦正在举办一场正式的晚宴。共有 $2n$ 人参加活动，他们以 $n$ 对（夫妻）的形式到场。经过一晚的欢乐后，艾伦希望将所有人排成一列拍摄最后的合影。这 $2n$ 人已排成一列，但艾伦对当前的排列不满意。他更希望每对夫妻在队列中占据相邻的位置，这样照片看起来更加美观。

请帮助艾伦计算：为使每对夫妻在队列中均占据相邻位置，他至少需要执行多少次相邻位置交换？

The first line contains a single integer $n$ ($1 \le n \le 100$), the number of pairs of people.

The second line contains $2n$ integers $a_1, a_2, \dots, a_{2n}$. For each $i$ with $1 \le i \le n$, $i$ appears exactly twice. If $a_j = a_k = i$, that means that the $j$-th and $k$-th people in the line form a couple.

第一行包含一个整数 $n$（$1 \le n \le 100$），表示情侣对的数量。

第二行包含 $2n$ 个整数 $a_1, a_2, \dots, a_{2n}$。对于每个满足 $1 \le i \le n$ 的 $i$，其在该序列中恰好出现两次。若 $a_j = a_k = i$，则表示队列中的第 $j$ 个人与第 $k$ 个人组成一对情侣。

Output a single integer, representing the minimum number of adjacent swaps needed to line the people up so that each pair occupies adjacent positions.

输出一个整数，表示使每对人占据相邻位置所需的最少相邻交换次数。

In the first sample case, we can transform $1 1 2 3 3 2 4 4 \rightarrow 1 1 2 3 2 3 4 4 \rightarrow 1 1 2 2 3 3 4 4$ in two steps. Note that the sequence $1 1 2 3 3 2 4 4 \rightarrow 1 1 3 2 3 2 4 4 \rightarrow 1 1 3 3 2 2 4 4$ also works in the same number of steps.

The second sample case already satisfies the constraints; therefore we need $0$ swaps.

在第一个样例中，我们可以用两步完成变换：$1 1 2 3 3 2 4 4 \rightarrow 1 1 2 3 2 3 4 4 \rightarrow 1 1 2 2 3 3 4 4$。注意，序列 $1 1 2 3 3 2 4 4 \rightarrow 1 1 3 2 3 2 4 4 \rightarrow 1 1 3 3 2 2 4 4$ 同样可在相同步数内完成。

第二个样例已满足约束条件；因此我们不需要任何交换（即需要 $0$ 次交换）。