#include <fstream>
using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
int v[10001],f[26];
int main() {
        int n,s=0;
        cin>>n;
        char c;
        for(int i=1; i<=n; i++) {
                cin>>c;
                c=c-'a';
                v[i]=c;
        }
        f[v[0]]++;
        for(int i=1; i<=n; i++) {
                for(int j=v[i]+1; j<26; j++)
                        s+=f[j];
                f[v[i]]++;
        }
        cout<<s;
        return 0;
}