#include<fstream>
#include<cstring>
using namespace std;
int n, i, j, L, s, m[30];
char ch[10003];
ifstream in("litere.in");
ofstream out("litere.out");
int main(){
    in>>n;
    in>>ch;
    m[ch[0]-96]++;
    for(i=1; i<n; i++){
        m[ch[i]-96]++;
        for(j=26; j>ch[i]-96; j--){
            s+=m[j];
        }
    }
    out<<s;
return 0;
}