CF46C Hamsters and Tigers

**题目大意：** 给你个**环**，环上有$n(2

第一行为一个整数$n$，表示点数 第二行为一个长度为$n$的字符串，其中$H$表示黑点，$T$表示白点

一个整数，即最少交换次数 感谢@守望 提供翻译

In the first example we shouldn't move anybody because the animals of each species already stand apart from the other species. In the second example you may swap, for example, the tiger in position $ 2 $ with the hamster in position $ 5 $ and then — the tiger in position $ 9 $ with the hamster in position $ 7 $ .