#include <fstream>
using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
int a[200];
int main()
{
    int i,j,sum=0,n,x;
    char c;
    cin>>n;
    for(i=1; i<= n; i++)
    {
        cin>>c;
        for(j=c+1; j<=c+27; j++)
            sum+=a[j];
        a[c]++;
    }
    cout<<sum;
    return 0;
}