You are given an integer n.

Let's define s(n) as the string "BAN" concatenated n

?times. For example, s(1) = "BAN", s(3) = "BANBANBAN". Note that the length of the string s(n) is equal to 3n.

Consider s(n). You can perform the following operation on s(n)

?any number of times (possibly zero):

Select any two distinct indices i and j (1≤i,j≤3n,i≠j).

Then, swap s(n)i and s(n)j.

You want the string "BAN" to not appear in s(n) as a subsequence. What's the smallest number of operations you have to do to achieve this? Also, find one such shortest sequence of operations.

A string a is a subsequence of a string b if a can be obtained from b by deletion of several (possibly, zero or all) characters.

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給定一個(gè)整數(shù) n。

讓我們將 s(n) 定義為字符串“BAN”連接 n

? 次。 例如，s(1) =“BAN”，s(3) =“BANBANBAN”。 請(qǐng)注意，字符串 s(n) 的長(zhǎng)度等于 3n。

考慮 s(n)。 可以對(duì) s(n) 執(zhí)行以下操作

? 任意次數(shù)（可能為零）：

選擇任意兩個(gè)不同的索引 i 和 j (1≤i,j≤3n,i≠j)。

然后，交換 s(n)i 和 s(n)j。

您希望字符串“BAN”不作為子序列出現(xiàn)在 s(n) 中。 要實(shí)現(xiàn)這一目標(biāo)，您需要執(zhí)行的最少操作次數(shù)是多少？ 另外，找到一個(gè)這樣的最短操作序列。

如果可以通過(guò)刪除幾個(gè)（可能是零個(gè)或全部）字符從 b 中獲得 a，則字符串 a 是字符串 b 的子序列。

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主要是判斷是奇數(shù)還是偶數(shù)，然后依次去交換即可。

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