#include <fstream>
using namespace std;
ifstream is ("litere.in");
ofstream os ("litere.out");

char v[10001];
int n, cnt;

int main()
{
    is >> n;
    for(int i = 1; i <= n; ++i)
    {
        is >> v[i];
        for(int j = 1; j < i; ++j)
        {
            if(v[j] > v[i])
                cnt++;
        }
    }
    os << cnt;

    return 0;
}