#include <fstream.h>
int b[28];
int main ()
{

ifstream f ("litere.in");
ofstream g ("litere.out");

char a;
int n,i,j;
long c=0;

f>>n;

while (f>>a)
{
b[a-'a']++;
for (i=a-'a'+1;i<=26; i++) c+=b[i];
}
g<<c<<'\n';

return 0;

}