反轉 ㄷㄷㄷㅈ - Problem

#18703. 反轉 ㄷㄷㄷㅈ

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AI Translation — This statement was translated using AI and may contain inaccuracies. Please refer to the original statement if in doubt.

UCPC 出題團隊在製作 D 題：ㄷㄷㄷㅈ 的測資時，發現要建立一個擁有許多頂點的 DUDUDUNGA-樹（DUDUDUNGA-tree）相當困難。給定 $N$，請寫一個程式來輸出一個擁有 $N$ 個頂點的 DUDUDUNGA-樹。

輸入格式

第一行給定樹的頂點數量 $N$。($6 \le N \le 300\,000$)

輸出格式

輸出 $N-1$ 行，每行包含兩個以空白分隔的整數，代表邊的兩個端點。頂點編號必須為 $1$ 到 $N$ 之間的整數。

範例

範例輸入 1

範例輸出 1

說明

DUDUDUNGA-樹的定義請參考 D 題：ㄷㄷㄷㅈ。對於輸入的 $N$，保證一定存在一個擁有 $N$ 個頂點的 DUDUDUNGA-樹。

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