#include <bits/stdc++.h>
#define all(a) (a).begin(), (a).end()
using namespace std;
using namespace chrono;

void solve() {
    int n; string s;
    cin >> n >> s;
    auto t = s;
    sort(all(t));
    auto u = t;
    reverse(all(u));
    int c1 = 0, c2 = 0;
    for (int i = 0; i < n; i++) {
        c1 += s[i] != t[i];
        c2 += s[i] != u[i];
    }
    cout << min(c1, c2)/2 << "\n";
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int t; cin >> t; while (t--)
        solve();
}