#include<fstream>
using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
int a[150],n,inter,i,j;
char sir;
int main()
{
 
          cin>>n;
          for(i=1;i<=n;i++)
                 {cin>>sir;
                 
                  a[sir-97]=a[sir-97]+1;
                  for(j=sir-96;j<=100;j++)
               
                  inter+=a[j];
                 }
cout<<inter;
return 0;
}