#include <bits/stdc++.h>

#pragma GCC optimize("Ofast")
using namespace std;

void solve(int cs) {
  int n;
  cin >> n;
  string s;
  cin >> s;

  array<int, 26> lc{}, rc{};
  for (int i = 0; i < n; i++) {
    rc[s[i] - 'a'] += 1;
  }

  int res = 0;
  for (int i = 0; i < n; i++) {
    lc[s[i] - 'a'] += 1;
    rc[s[i] - 'a'] -= 1;
    for (int j = 0; j < 26; j++) {
      if (lc[j] > 0 && rc[j] > 0) {
        if (lc[j] == rc[j]) {
          if (j != (s[i] - 'a')) {
            res += 1;
            break;
          }
        }
      }
    }
  }
  cout << res << "\n";

}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int tc = 1;
  cin >> tc;
  for (int cs = 1; cs <= tc; cs++) {
    solve(cs);
  }
  return 0;
}