//calcularea numarului de inversiuni
#include <fstream>

#define In "litere.in"
#define Out "litere.out"
#define Nmax 10004

using namespace std;
int N;
int nr[256];
long long sol;
int main()
{
    int i,j;
    char ch;
    ifstream f(In);
    f >> N;
    for(i = 1;i <= N;i++)
    {
        f >> ch;
        nr[int(ch)]++;
        for(j = ch+1;j<='z';j++)
            sol += nr[j];
    }
    f.close();
    ofstream g(Out);
    g<<sol<<"\n";
    g.close();
    return 0;
}