#include<fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,m,i,j,k,ok,minim,s,v[250],y;
char maxim,x;
int main(){
    fin>>n;
    for(i=1;i<=n;i++){
        fin>>x;
        y=x+0;
        v[y]++;
        for(j=y+1;j<='z';j++)
            s+=v[j];
    }
    fout<<s;
    return 0;
}