#include <fstream>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,t;
char ch[10001];
int main()
{
    fin>>n;
    for(int i=0;i<n;++i)
    {
        fin>>ch[i];
        for(int j=i-1;i>=0;--j)
            if (ch[i]<ch[j])t++;
    }
    fout<<t;
}