#include <bits/stdc++.h>
#define int long long
using namespace std;

signed main() {
  int t; cin >> t;
  while (t--) {
    int n, ans (0); string s;
    cin >> n >> s;
    map<char,int> L, R;
    for (auto& x:s) R[x]++;
    for (auto& x:s) {
      L[x]++; R[x]--;
      for (char c('a'); c <= 'z'; c++) {
        if ((L[c] == R[c]) && (c != x) && L[c] != 0) {
          ans++; break;
        }
      }
    }
    cout << ans << '\n';
  }
}