CF1914A Problemsolving Log

Monocarp is participating in a programming contest, which features $ 26 $ problems, named from 'A' to 'Z'. The problems are sorted by difficulty. Moreover, it's known that Monocarp can solve problem 'A' in $ 1 $ minute, problem 'B' in $ 2 $ minutes, ..., problem 'Z' in $ 26 $ minutes. After the contest, you discovered his contest log — a string, consisting of uppercase Latin letters, such that the $ i $ -th letter tells which problem Monocarp was solving during the $ i $ -th minute of the contest. If Monocarp had spent enough time in total on a problem to solve it, he solved it. Note that Monocarp could have been thinking about a problem after solving it. Given Monocarp's contest log, calculate the number of problems he solved during the contest.

The first line contains a single integer $ t $ ( $ 1 \le t \le 100 $ ) — the number of testcases. The first line of each testcase contains a single integer $ n $ ( $ 1 \le n \le 500 $ ) — the duration of the contest, in minutes. The second line contains a string of length exactly $ n $ , consisting only of uppercase Latin letters, — Monocarp's contest log.

For each testcase, print a single integer — the number of problems Monocarp solved during the contest.