cf 1552A

#include<bits\stdc++.h>

using namespace std;

int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        int n;
        scanf("%d", &n);
        string s;
        cin >> s;
        string s1 = s;
        sort(s1.begin(), s1.end());
       //cout << s << s1;
        int cnt = 0;
        for(int i = 0; i < n; i++)
        {
            if(s[i] != s1[i]) cnt++;
        }
        printf("%d\n", cnt);
    }
}