#include <fstream>

using namespace std;

int n,i,nr,ok,s,j,f[26];

char v[10001],aux;

ifstream fin ("litere.in");

ofstream fout ("litere.out");

int main (){

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

        for (j=v[i]-'a'+1;j<=25;j++){
            s+=f[j];
        }

        f[v[i]-'a']++;
    }

    fout<<s;


    return 0;
}