Score : $200$ points

问题描述

我们有 $4$ 张卡片，每张上面写有整数 $1$，$4$ 张卡片写有 $2$，……，$4$ 张卡片写有 $N$，总共是 $4N$ 张卡片。

高桥洗乱了这些卡片，从中移除了一张，并把剩下的 $4N-1$ 张卡片堆交给你。这堆卡片中的第 $i$ 张（$1 \leq i \leq 4N - 1$）上写有一个整数 $A_i$。

找出被高桥移除的那张卡片上的整数。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

We have $4$ cards with an integer $1$ written on it, $4$ cards with $2$, $\ldots$, $4$ cards with $N$, for a total of $4N$ cards.

Takahashi shuffled these cards, removed one of them, and gave you a pile of the remaining $4N-1$ cards. The $i$-th card $(1 \leq i \leq 4N - 1)$ of the pile has an integer $A_i$ written on it.

Find the integer written on the card removed by Takahashi.

Constraints

• $1 \leq N \leq 10^5$
• $1 \leq A_i \leq N \, (1 \leq i \leq 4N - 1)$
• For each $k \, (1 \leq k \leq N)$, there are at most $4$ indices $i$ such that $A_i = k$.
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

$N$

$A_1$ $A_2$ $\ldots$ $A_{4N - 1}$

Output

Print the answer.

Sample Input 1

3
1 3 2 3 3 2 2 1 1 1 2

Sample Output 1

3

Takahashi removed a card with $3$ written on it.

Sample Input 2

1
1 1 1

Sample Output 2

1

Sample Input 3

4
3 2 1 1 2 4 4 4 4 3 1 3 2 1 3

Sample Output 3

2

update @ 2024/3/10 10:13:17