Score : $150$ points

问题陈述

有 $2N$ 个人排成一行，从左边数第 $i$ 个人穿着颜色为 $A_i$ 的衣服。这里，衣服有 $N$ 种颜色，从 $1$ 到 $N$，每种颜色恰好有两个人穿着。

找出有多少个整数 $i=1,2,\ldots,N$ 满足以下条件：

• 在穿着颜色为 $i$ 的两个人之间恰好有一个人。

以上为大语言模型 kimi 翻译，仅供参考。

Problem Statement

There are $2N$ people standing in a row, and the person at the $i$-th position from the left is wearing clothes of color $A_i$. Here, the clothes have $N$ colors from $1$ to $N$, and exactly two people are wearing clothes of each color.

Find how many of the integers $i=1,2,\ldots,N$ satisfy the following condition:

• There is exactly one person between the two people wearing clothes of color $i$.

Constraints

• $2 \leq N \leq 100$
• $1 \leq A_i \leq N$
• Each integer from $1$ through $N$ appears exactly twice in $A$.
• All input values are integers.

Input

The input is given from Standard Input in the following format:

$N$

$A_1$ $A_2$ $\ldots$ $A_{2N}$

Output

Print the answer.

Sample Input 1

3
1 2 1 3 2 3

Sample Output 1

2

There are two values of $i$ that satisfy the condition: $1$ and $3$.

In fact, the people wearing clothes of color $1$ are at the 1st and 3rd positions from the left, with exactly one person in between.

Sample Input 2

2
1 1 2 2

Sample Output 2

0

There may be no $i$ that satisfies the condition.

Sample Input 3

4
4 3 2 3 2 1 4 1

Sample Output 3

3