#include <fstream>
#include <algorithm>
using namespace std;
long long n,i,j,rez,d,s,m,x;
char nr;
int f[125];
ifstream cin("litere.in");
ofstream cout("litere.out");
int main() {
    cin>>n;
    for(i=1;i<=n;i++){
        cin>>nr;
        for (j=nr+1;j<=122;j++) {
            rez+=f[j];
        }
        f[nr]++;
      }
      cout<<rez;
}