#include <fstream>

using namespace std;

int n, i, j, sol, nr[10001];
char v[10001];

ifstream fin("litere.in");
ofstream fout("litere.out");

int main(){
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];

    for(i=n-1;i>0;i--){
        if(v[i] == v[i+1] && i!=n)
            nr[i] = nr[i-1], sol+=nr[i];
        else
            for(j=n;j>i;j--)
                if(v[j]<v[i])
                    sol++, nr[i]++;

    }
    fout<<sol<<"\n";

    return 0;
}