Minimum Cost to Balance a String

You are given a string (S) of length (N) consisting only of the characters A, B, and C. The task is to convert (S) into a balanced string where each character appears exactly (\frac{N}{3}) times. A conversion operation involves changing any character to any other among those allowed. The cost of a transformation operation is (1) per change. Compute the minimum transformation cost required for balancing the string.

Note: It is guaranteed that (N) is divisible by (3).

inputFormat

The input is read from standard input (stdin) and consists of two lines:

1. The first line contains an integer (N), the length of the string.
2. The second line contains the string (S) of length (N), consisting only of characters A, B, and C.

outputFormat

Output to standard output (stdout) a single integer — the minimum cost required to transform the string into a balanced string where each character appears exactly (\frac{N}{3}) times.## sample

6
AAABBB

2