#include <iostream>
#include <fstream>
 
std::ifstream in ("litere.in");
std::ofstream out ("litere.out");
 
unsigned int frLit[26];
 
int main()
{
    int n;
    in >> n;
    int nrInv = 0;
    for(int i = 0; i < n; i++)
    {
        char t;
        in >> t;
        t-='a';
        frLit[t]++;
        for(int j = t+1; j < 26; j++)
            nrInv+=frLit[j];
    }
    out << nrInv;
}