#include <iostream>
#include <fstream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
const int N=10001;
int n;
char s[N];
int v[30];
int main()
{
    int x=1,nr=0;
    char aux;
    in>>n;
    in>>s;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<27;j++)
        {
            if(s[i]-'a'>j)
                v[j]++;
        }
        nr+=v[s[i]-'a'];
    }
    out<<nr;
    return 0;
}