#include<fstream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int a[101],m,n;
int main()
{
    int i,j;
    char s;
    in>>m;
    for(i=1;i<=m;i++)
{
    in>>s;
    a[s-97]=a[s-97]+1;
    for(j=s-97+1;j<=25;j++)
    n=n+a[j];
    }
out<<n<<"\n";
return 0;
}